PURPOSE: To prevent an error rate from being made excessive by the use of a fault memory block by inspecting and correcting an error in a memory.

CONSTITUTION: A memory module is divided into segments and before data are written, the accumulation of errors is detected by inspecting the memory 1. When any error is accumulated, that segment is not used for storing data and after the end of a fixed period following the write of data, each segment is inspected concerning a single error 3. When the single error exists, the corrected data are written in the segment 2 and the inspection of the single error is repeated until no error is detected.