PURPOSE:To eliminate the need for the storage of large capacity and to eliminate special processing to obtain an access frequency by providing a switch to feed a current from a constant current power source to a charge accumulating element in an oblivious type addition storage when a writing instruction is executed by a writing controller. CONSTITUTION:An access frequency observing device is provided an oblivious type additional storage 50 and a writing controller 40 and the oblivious type additional storage 50 has a constant current power source circuit 340. Further, at every address charge accumulating elements 321 and 331 and a switch 110 by which the current from a constant power source is fed to the charge accumulating elements 322 and 332 in case of instruction of writing by the writing controller 40 are provided. Thus, the storage device of the large capacity is eliminated and the access frequency observing device which does not need the special processing to obtain the access frequency can be realized.
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