PURPOSE: To ensure the strict control for the time of replacement of a read-only memory (E2PROM) which can be electrically erased and written, by accumulating and storing the write indicating signals to be applied to the E2PROM in response to the address of the E2PROM.

CONSTITUTION: A center device 20 controls terminal devices set at four remote areas and transmits data. The terminal devices have prescribed actions based on the transmitted data. The address signals ADR and write enable signals WE' transmitted to E2PROMs 11W14 from the device 20 are also sent to an E2PROM set opposite to the device 20. The erasing/writing frequencies carried out by the center 20 for addresses corresponding to E2PROMs 11W14 are written and stored to the address which is designated by the E2PROM10 with the signal ADR. The number bit 17 for each word of the E2PROM10 can cover the upper limit values 104W105 of rewritable frequencies of E2PROMs 11W14. Such rewriting frequencies stored in the E2PROM10 are read out to outside when necessary as the read data RDT and used as the maintenance data for necessary counterplans.