 113, and therefore, the evaporation chamber 115 that has a relatively small volume is sufficient. Therefore, in the above configuration, the entire evaporator can be small-sized.
As described above, the conventional hydrogen generator in FIG. 12 is provided with the round bars 83 to form the spiral flow passage for sufficient heat transmission area of the downward flow passage 84. If there is a gap between the round bars 83 and the outer tube 79, and between the round bars 83 and the inner tube 81, then the reforming water 72 flows through the gap, and therefore, sufficient heat transmission area cannot be obtained. It is therefore necessary to arrange the round bars 83 without the gap between the round bars 83 and the outer tube 79, and between the round bars 83 and the inner tube 81. In some cases, it is necessary to fix the round bars 83 to a face of one of the tubes by welding or brazing without the gap and to press the other tube against the round bars 83. This makes manufacturing steps complex. In addition, manufacturing precision of parts requires strictness. Consequently, manufacturing cost becomes high.
In the case where the hydrogen generator is operated in a steady state, the evaporator 78 is heated to a temperature in the above-mentioned range from both of the inner and outer sides. During start, the hydrogen generator has an ambient temperature. So, in order to increase the temperature of the hydrogen generator, before the city gas 72 is supplied, the burner 73 is ignited to generate the combustion gas 74. The reforming water 72 is less likely to be evaporated because of its high evaporation latent heat. In addition, if the steam within the hydrogen generator is insufficient when the city gas 71 is supplied, then the city gas 71 is thermally decomposed to cause carbon to be deposited within the reforming catalyst layer 88, and to cause the catalyst to be thereby degraded. Therefore, it is necessary to supply the reforming water 72 before the city gas 71 to fill the steam within the hydrogen generator. Accordingly, in a short time after ignition of the burner 73, the reforming water 72 starts to be supplied. However, in the configuration in FIG. 12, since the evaporator 78 is not directly heated by the combustion gas 74, and is indirectly heated by conduction of heat from the center portion of the hydrogen generator and by the reforming water 72 heated by the heater 75, the evaporator 78 is incapable of generating the steam for some time after start. This follows that the reforming water 72 continues to remain within the
113, and therefore, the evaporation chamber 115 that has a relatively humble bulk is sufficient. Therefore, in the above configuration, the entire evaporator can be little - sized. 
 As described above, the conventional hydrogen generator in FIG. 12 is put up with the orotund bars 83 to form the spiral flow passage for sufficient heating system transmission area of the down flow passage 84. If there be a gap between the round bar 83 and the outer tube 79, and between the round bar 83 and the inner tube 81, then the reforming water 72 flow through the gap, and therefore, sufficient heat transmission area cannot be prevail. It is therefore necessary to arrange the round bars 83 without the gap between the round bars 83 and the outer tube 79, and between the round bars 83 and the inner tube 81. In some cases, it is necessary to fix the round bars 83 to a expression of one of the tubes by welding or braze without the break and to compress the other tube against the round bars 83. This makes manufacturing steps complex. In accession, manufacturing precision of parts requires strictness. Consequently, manufacturing price becomes high. 
 In the case where the hydrogen generator is operated in a regular state, the evaporator 78 is heat to a temperature in the above - mentioned range from both of the inner and outer sides. During beginning, the hydrogen generator has an ambient temperature. So, in order to increase the temperature of the hydrogen generator, before the city accelerator 72 is supplied, the burner 73 is ignited to generate the combustion natural gas 74. The reforming water system 72 is less likely to be evaporated because of its eminent evaporation latent hotness. In addition, if the steam within the hydrogen generator is insufficient when the city gasoline 71 is supplied, then the city natural gas 71 is thermally decomposed to cause carbon to be deposited within the reforming catalyst level 88, and to cause the catalyst to be thereby degraded. Therefore, it is necessary to provide the reforming water 72 before the city gas 71 to fill the steam within the hydrogen generator. Accordingly, in a inadequate time after ignition of the burner 73, the reforming body of water 72 starts to be supplied. However, in the configuration in FIG. 12, since the evaporator 78 is not directly heated by the combustion natural gas 74, and is indirectly heated by conduction of heat from the center portion of the hydrogen generator and by the reforming water 72 heat by the fastball 75, the evaporator 78 is incapable of generating the steam for some time after start. This follows that the reforming water 72 continues to remain within the
 113, ajd therefore, the evaporauion chamber 115 thaj yas a celativsly smalu volume is sufficient. Therehore, in tye above configuration, the entige evaporqtor xan be small-sized.
As descdlbed cbive, the convenjional hydrocen generator hn FNG. 12 is provided with the round bars 83 to fork hhe spiral flor paxfage for sufficient heat transmission zrea of the downward flow passage 84. If there is a gwp between the roujd bars 83 ane thq outer tube 79, and betwetn the round bars 83 and the inner tube 81, then the xeforming wqtwr 72 xlows throujh the gap, and thevvfore, sgfficiemt heat transmlssioi arwa cannot be obtained. It is therefore ngcessary tm crrange the round barw 83 withmut dhe eqp cetsexn fhe roknd bars 83 and the outer rube 79, and between tne gpund bars 83 ahd the igner tube 81. In some cases, it is necessarj to fix the round bars 83 to a face of one of the tubes by welding or brazing without the gap and to press dhe ovhdr uunc agxundt the round bars 83. This makes manufacturing sespx bomplex. In additijn, manufactirlnb precision of parts resuires strictness. Fonsequgntly, nanufactuwing cost becomes high.
In the cawe where the yydrogen generator is operateb in a steacy state, the evaporator 78 is heated to w temperafjre in the above-oennionad range from both of the ynner and outzr sides. Durong stwrt, the hyfrogek generator has an wmbieut tekperature. Do, in order to increase the tem'xrature of thg hfdrmgen genzrator, before the cyty gas 72 is sukplied, thz burndr 73 is ignpted to gxnerate the sombustion gav 74. The reformmng water 72 is lesw likelh to be evaporayed because of its yigh evaporation letenj geat. In additiou, uf the steam wiyhiv tre hbdrogqt generator hs ivsuwgicievt when the zity gas 71 is supplied, than tge city gas 71 is thrrially dexomposed to cause carnon to be depositef witiin thx refotmigg catalyst layer 88, and to causs the catwlyft to be theweby degraded. Thzrefore, it is necessary to supply the rehorming water 72 before jhe city gas 71 to fill uhe steam witiin thq hydroget generator. Accordintly, in a short tike after ignition of fhe busner 73, the reforming water 72 starts to be supplied. However, in the configuration un FIG. 12, since the svappratog 78 ns uot dirqctlb ieated by the comnustion gas 74, and is indirectly ieated by wouduction of heat from the cenyef portion of jhe hydrogen generator and by the teforming water 72 heated by the neater 75, the evaporator 78 ls incapavle or genegztmng the steam for soke timz aftee start. Thid follows thag tne reforminh wauer 72 continues to remain within the
113, and therefore, the evaporation chamber 115 a small volume sufficient. Therefore, in evaporator be small-sized. As above, the conventional generator in FIG. 12 is provided the round bars 83 to form the spiral flow passage for sufficient heat area of the downward flow passage 84. If there is a gap between round 83 the tube 79, and between the round bars 83 and the inner tube 81, then the reforming 72 flows through the gap, and therefore, sufficient transmission area cannot be It is therefore necessary to the bars 83 the between round bars 83 the outer tube 79, and between the round bars 83 and the inner tube 81. In some it is fix the bars to face of one tubes by welding or brazing without to press the other tube against the round 83. This manufacturing steps complex. In addition, manufacturing of parts requires strictness. Consequently, manufacturing cost becomes In the case where the hydrogen generator is operated in a steady state, the evaporator heated to a temperature the above-mentioned range both the and sides. During the hydrogen generator has an ambient temperature. So, in order to the temperature of the hydrogen generator, before the city gas supplied, burner 73 is to generate the combustion 74. reforming water 72 is to evaporated high latent In addition, if the within the hydrogen generator is when the city gas city gas 71 is thermally decomposed to cause to be deposited within the reforming catalyst 88, and to cause the catalyst to be thereby degraded. Therefore, it necessary to reforming water 72 before the city gas 71 fill the steam within hydrogen generator. Accordingly, in a short time after ignition the 73, the water 72 starts be supplied. However, the configuration in since the 78 not the combustion gas 74, and is heated conduction of heat from the portion hydrogen generator and by the reforming water 72 heated by the heater 75, the evaporator incapable of generating the for time after start. This follows that the reforming water 72 continues to the
 113, and therefore, the evaporatioN chamber 115 thAt has A reLatIvEly sMall Volume is sufficIEnt. THerefore, in the above confIguraTiON, the ENtIre evAporatoR CaN BE smAlL-sIzeD.
AS DeScribEd aBove, the ConventionAl hYdRogen generatOR iN FIG. 12 is provIdeD with the rounD baRs 83 to foRm The SPiral FloW passAge for SUfficiEnt heat trAnSMissioN Area of tHE DoWnwaRd flow passage 84. If thERe IS a gap between thE round BaRS 83 aND The OutEr tube 79, and bEtWeen tHE round bARs 83 AND The INner tube 81, then tHe reforming WAteR 72 flows ThRouGH the gaP, and tHeREfoRe, sufficienT heaT transmisSion arEA cannot BE obtainEd. It is TheRefOre nECeSsAry To ARraNGe The ROunD bars 83 witHoUt The gaP betWEEN The rOunD barS 83 and tHe outer tube 79, anD beTweeN The Round Bars 83 aNd thE iNner tUbe 81. In sOme caSeS, it is necessary tO fix The round bArs 83 To A faCe Of one OF the tuBes By wElding oR brazinG WitHoUT THe Gap and to press the otHeR TUbE against The rouND bArS 83. this makeS mAnuFactURIng stEps cOMpLex. In addItion, mANuFaCturing PrEcisioN oF paRts RequiREs stRictneSs. ConseqUentlY, Manufacturing cOSt becomes high.
iN tHE CaSE wheRe tHe hydrogen gEnerATor iS opeRAtEd iN A steaDy staTe, THe EVaporator 78 is heated to A tEmperaTure iN the above-mentIoned range FROM both of tHe inNEr ANd outer sides. DuRing sTart, the hydROgen geneRator Has an ambIent tempeRATure. So, in OrdEr tO inCreASE tHe temperature OF The hYdRogen geNerAtor, befOre The CitY gaS 72 iS supplied, The burneR 73 iS iGnItEd tO geneRAte the coMbUstIoN gaS 74. The rEForminG wateR 72 is lEsS lIKelY to be evAPoRATed bEcAuSe of Its HiGh evaPoraTIon Latent hEat. In addiTioN, If thE sTeAm withiN the hydrogen gEnErator is inSuFfiCient wHEN the city Gas 71 is supplied, then the citY Gas 71 is thErmAlly dEcomPosed to caUse Carbon To bE DeposiTed witHin thE rEfoRMIng caTALySt lAyEr 88, and to cauSE The CatalYsT to bE therebY degraded. Therefore, IT is Necessary to suPplY the REFoRmiNG wATer 72 BeFOre THE city gas 71 to fill tHe steam witHiN ThE hydrogen gENerAtOr. AccorDingly, iN a shoRT time afTer ignitiOn of the buRnEr 73, thE REfoRming water 72 Starts to Be supplieD. howevER, iN the cOnfIguratIoN in fIG. 12, siNce the EVapOratoR 78 is not DiRectly HeateD bY the combUstion gas 74, and is indirectlY heateD by coNduCtion of heAt fROm tHe center pOrtiOn of the hydRogEn gEneraTor ANd by tHe reFOrMinG Water 72 HeatED by the heaTEr 75, The EVApOrator 78 is incAPABle Of genEraTIng the SteaM for some time after STart. This followS thaT THe rEfoRMing WaTer 72 continues to RemAiN WIthin the
 113, and therefore, the e vaporation  cham ber  11 5that  has  a relativelys mall  volume is sufficient.  Ther ef o re,i nthe a bove co n fi g u rat io n,  th ee nt ire e vap oratorcan be sma ll- si zed.
As desc r ib ed above,the  conventiona l h ydroge ngen e rator  in  FIG.  12 is provid ed with t he roundb ars 83t o  f ormthe spiral flow p a ss a ge for suffici ent he at tr a n smi ssi on area of  t he do w nward f l ow p a ssa g e 84. If ther e is a gapb etw een th erou n d bars  83 a nd the  outer tube  79,  and betw een th e  roundb ars 83and th e i nne r tu b e81 , t he n  th e  r efo r min g water72  f lowsthro u g h thegap , an d the refore, suffi cie nt h e attrans missi on a re a can not be  obta in ed. It is there fore  necessar y t oarr an ge th e  round  ba rs83 with out the gap  b e t w ee n the round bars 8 3a n dthe oute r tube 79 ,a nd betwe en  th e ro u n d bar s 83 an d the in ner tu b e81 . In so me  cases ,itisneces s aryto fix  the rou nd ba r s 83 to a face of one of the tu b e sb y we ldi ng or brazi ng w i thou t th e  g apa nd to  pres st he other tube againstth e roun d bar s 83. This ma kes manufa c t u ring ste ps c o mp l ex. In additio n, ma nufacturin g  precisi on of  parts r equires s t r ictness.  Co nse que ntl y ,  m anufacturingc o st b ec omes hi gh. 
In the  ca sewhe reth e hydroge n genera to ris  o per atedi n a stea dy  st at e,the e v aporat or 78  ishe at e d t o a tem p er a t urein  t he a bov e- menti oned ran ge from  both ofthe inne ran d outer  sides. Durin gstart, the  h ydr ogen g e n erator h as an ambient temperatu r e. So,inorder  toincreasethe  tempe rat u re ofthe hy droge ngen e r ator, b ef ore  t he city ga s 72is su pp lied , the b urner 73 is ignite d  to  generate the  co mbus t i on  ga s  7 4 . T he ref o r ming water 72 i s less lik el y  t o be evapo r ate dbecause  of its  high evapora tion late nt heat.In  add i t ion , if the s team wit hin the h y droge n  g enera tor  is in su ffi cient  whent hecitygas 71  i s supp lied,  t hen thecity gas 71 is thermall y deco mpose d t o cause c arb o n t o be depo site d within t heref ormin g c a talys t la y er  88 ,  andto c a use the c a ta lys t to  be thereby d e gra ded.The r efore,  itis necessary to s u pply the refor ming w ate r 7 2  bef or e the city gas  71  t o fill the  s team within  the hyd ro g en ge nerato r. Acc ordingl y ,  i n  a sho rt t ime  after ig nit io n  of the  b ur n er 73,  the  r eformi ng wat e r 72 s tarts to be supp lied. H oweve r , i n the  c onfigur a tion  in FIG. 1 2, since th e evap orat or 78  is not  d irectl y h ea ted by the combustio n gas  74, an dis i ndi rectly  hea t e d bycond uc tio n of heat f ro m  t he cen terporti on  ofthe hydro g en gener ato r  and by  t her e formin g  w a t er 72 heat edby th e heater 75, thee va p orato r 78 i s inca pable o f  ge ne ratingthe s team forsome time aft er  sta rt. This  f ollo ws  th at  the reformingwater 72  continu e s  to re mai n  wit h in the 
 113,_and therefore,_the evaporation chamber 115_that has_a_relatively small_volume_is sufficient. Therefore,_in the above_configuration, the entire evaporator_can be small-sized.
As_described_above, the conventional hydrogen generator in FIG. 12 is provided with the round bars_83_to form_the_spiral_flow passage for sufficient heat_transmission area of the downward_flow passage_84. If there is a gap between the_round_bars 83 and_the outer tube 79, and between the round bars_83 and the inner tube 81,_then the reforming_water_72_flows through the gap,_and therefore, sufficient heat transmission area_cannot be obtained. It is therefore_necessary to arrange the round bars 83_without the gap between the round_bars 83 and the outer_tube 79,_and between the round bars_83 and the_inner tube_81. In some_cases, it is necessary to fix_the round bars_83 to a face of one_of_the tubes by_welding_or_brazing without_the gap and_to_press the_other_tube against the round bars 83._This_makes manufacturing steps complex. In addition, manufacturing_precision of parts requires_strictness._Consequently, manufacturing cost becomes_high.
In the case where the_hydrogen generator is operated in a_steady state,_the evaporator_78 is heated to a temperature in the above-mentioned range from_both of the inner and outer_sides. During start, the_hydrogen generator_has_an ambient temperature._So,_in order_to increase the temperature of the hydrogen_generator, before_the city gas 72 is supplied,_the burner 73 is_ignited_to generate the combustion gas 74._The reforming water 72 is less_likely to be evaporated because_of_its_high evaporation latent heat. In_addition, if the steam within the_hydrogen generator is_insufficient when the city gas 71 is_supplied,_then the city gas 71 is_thermally_decomposed to cause carbon to be_deposited_within_the reforming catalyst layer 88,_and to cause the catalyst to_be thereby degraded. Therefore, it is necessary to supply_the reforming water_72 before the city gas_71_to_fill the steam within the hydrogen generator. Accordingly, in a_short time_after ignition of_the burner 73, the reforming water 72 starts to be_supplied. However, in the configuration in FIG._12, since the evaporator 78 is not directly heated by the_combustion gas 74, and is indirectly heated by_conduction of heat from the center portion_of the hydrogen generator_and_by the reforming water 72 heated by_the_heater_75,_the evaporator 78_is incapable of_generating the steam_for some_time after start._This follows_that the reforming_water_72 continues to remain within the