1. A vehicle-mounted electronic control apparatus comprising: a main power supply circuit that is fed with electric power from an on-board battery to generate a first stabilized control voltage when a power switch is closed; an auxiliary power supply circuit that is directly fed with electric power from said on-board battery to generate a second stabilized control voltage without regard to the opening and closing of said power switch; a control CPU composed of a microprocessor including a nonvolatile control memory in which a control program and a reference control constant are written; and a volatile backup memory that is always fed with electric power through said main power supply circuit or said auxiliary power supply circuit so as to store learned correction data for said reference control constant stored in said nonvolatile control memory; wherein said control CPU is connected to a plurality of input sensors and a plurality of electric loads, and is fed with electric power through said main power supply circuit so as to control said plurality of electric loads in response to contents of said nonvolatile control memory and the operating state of said input sensors; wherein said apparatus further comprises a power supply turn-on detection circuit having a rising differentiating circuit for an input voltage or an output voltage of said auxiliary power supply circuit, and a power supply interruption monitoring memory that is reset by the output of said rising differentiating circuit; wherein said apparatus further comprises: initialization means for initializing said backup memory; initialization completion storage means for storing an initialization completion state of said initialization means; initialization storage verification means for verifying an initialization completion storage state of said initialization completion storage means; hierarchization abnormality detection means for detecting the presence or absence of an abnormality in the storage contents of said backup memory using a plurality of abnormality detection processes; and abnormality detection selection means for selecting and determining which one or more of the abnormality detection processes of said hierarchization abnormality detection means should be executed; wherein said power supply turn-on detection circuit stores the existence of a power supply interrupted state into said power supply interruption monitoring memory by putting the contents of said power supply interruption monitoring memory into a reset state in response to when said auxiliary power supply circuit is connected to said on-board battery; wherein said hierarchization abnormality detection means executes a plurality of abnormality detection processes including at least a first abnormality detection process, and each of said abnormality detection processes estimates or detects whether there is an abnormality in the memory contents of said backup memory; wherein said first abnormality detection process makes, in response to when said power supply interruption monitoring memory has not stored a set state, a determination that stored information of said backup memory has been lost; wherein said initialization means initializes said backup memory by said control CPU when said hierarchization abnormality detection means has estimated that there is an abnormality in the contents of said power supply interruption monitoring memory; wherein said initialization completion storage means rewrites and changes the contents of said power supply interruption monitoring memory into a set state in response to when said control CPU has completed the initialization of said backup memory, and at the same time, verifies, using said initialization storage verification means or a voltage monitoring signal that an initialization completion state has been stored; wherein said initialization storage verification means reads out and verifies whether the rewriting and changing of said power supply interruption monitoring memory has been executed to change the reset state into a set state; wherein said voltage monitoring signal inputs a drive power supply voltage for said power supply interruption monitoring memory to said control CPU whereby said control CPU verifies the storage of initialization by the presence or absence of said voltage monitoring signal, and if the drive power supply voltage has not been supplied to said control CPU, verifies and determines that the storage of initialization has not been made; and wherein said abnormality detection selection means operates in such a manner that immediately after said power switch has been turned on, only some of the abnormality detection processes including said first abnormality detection process of said hierarchization abnormality detection means are executed, while omitting execution of remaining abnormality detection processes in said hierarchization abnormality detection means, and during operation of said control CPU except for immediately after the turning-on of said power supply, a plurality of the remaining abnormality detection processes are repeatedly executed in a periodicity no more than a predetermined period.