1. A translation server for providing a translating function to a client via a network, comprising: a translation user interface control unit which receives a translating request from a user interface provided for said client and activates a translating process; an original sentence obtaining unit which accesses an address designated in said translating request and obtains an original sentence file; a translation executing unit which executes machine translation of said original sentence file by using a translation dictionary designated in said translating request; and a cache processing unit which searches a translated sentence cache file of a header matched with said translating request from a translated sentence cache database and transmits translated sentence cache data to said client, and if said translated sentence cache file cannot be searched, preliminarily registers the translated sentence cache file in which only the header matched with said translating request has been stored into said translated sentence cache database, thereafter, sets a cache state into “during translation”, allows said translation executing unit to translate said original sentence file, transmits a translation result to said client, stores said translation result into said translated sentence cache file which has preliminarily been registered, and sets the cache state into “available”.