PURPOSE: To check easily the storage content of a memory without increasing the memory capacity, by comparing a result of a prescribed operation obtained by reading the storage data on each word region with the reference data to discriminate.

CONSTITUTION: A memory 2 to be checked is set in a prescribed state, and at the same time the reference data is set to a register 71 in response to the storage data of the memory 2. Then a CPU1 is started. The storage data of the memory 2 are supplied to the CPU1 and added successively to each other to be stored temporarily. When this addition is over, the address information corresponding to a word region 2N of the memory 2 is delivered. Then the reference data is fetched into the CPU1, compares the result of addition which is stored temporarily with the reference data. The stored data is decided normal if the coincidence is obtained from the comparison and then decided abnormal if no coincidence is obtained. Thus the storage contents of a memory can be easily checked without increasing the memory capacity.