PURPOSE: To prevent the occurrence of a software error due to a radioactive particle by reading a nondestructive readout type memory cell, holding information temporarily and comparing with reread information, and reading the cell again and outputting information when the information is different.

CONSTITUTION: The information bit in a memory cell 20 in a nondestructive readout type memory cell array 11 is read out through a sense amplifier and stored in a temporary storing means 14, and the bit is compared with a reread information bit by a comparing meands 15. A writing and reading control means 16 is controlled through the means 15; when the comparison result shows coincidence, the reread bit information is outputted and when not, the cell 20 is read again through the sense amplifier to output read bit information. The period of three-time sense amplifier operation is longer than the period wherein the influence of radioactive particles remain, so a software error due to the radioactive particle is prevented from occurring.