PURPOSE: To assure a positive operation of a non-volatile memory by a method wherein the number of operations of revising data in the non-volatile memory is counted every time the revising is carried out and as the number of revising exceeds a predetermined number of times, the data is transferred to a non-used area.

CONSTITUTION: An address to be stored is read out from a non-volatile memory 2, stored in an index register 6, the number of times of revising is read out from the memory 2 and stored in a CNT register 7. The number of times of revising is increased by one and it is tested if the revising time exceeds a revising assurance time, for example, 10,000 times. If the times do not exceed it, the revising times increased by one and the cooking data are written into the same area. If it is judged that the times exceed 10,000 times, the revising times exceed the assurance value, resulting in that it is required to write data in a new area. Then, the last area in the area being operated at present is searched out. That is, all the addresses to be stored are read out for all the cooking numbers so as to get their maximum value. Number of data is added to the maximum value and the added value is stored in a register 6. In this case, the register 6 indicates a leading address in the area not being used.