PURPOSE: To increase the overall lifetime of a memory to which the replacement frequency of contents of an EEPROM, etc. is limited, by performing the replacement of contents with an approximately equal frequency for each address.

CONSTITUTION: A data code DC0 is stored to a head address #0 of a code area CE, and the end marks EM are stored to both head addresses #1 and #2 follow ing the address #0. Then the corresponding data DT0 is stored to plural continu ous addresses with the head address of a data area DE defined as a standard. When data are stored, a data code DC1 is stored to the address #1 after replace ment of the contents. At the same time, the mark EM is stored to the address #3. The data DT1 is stored to each address following the data DT0. Hereafter the similar operations are repeated. The storage of 1 time is carried out to addresses #0 and n+2; while the storage of 2 times are carried out to addresses #1Wn+1 respectively. Then the storage of one time is carried out to each address of the area DE. Thus the storage frequencies are averaged.