PURPOSE: To inhibit an optional number of bytes from being written from an optional point of time by providing every byte corresponding to a specific address with a write control bit and generating a write control signal until writing execution.

CONSTITUTION: One byte of an E2PROM consists of one bit 1 for write control and (n) bits for DATA2. When a write instruction 11 is issued, a bit read circuit 3 for control reads a control bit value out of an address-specified byte after address setting and sets or resets a write flag 5. When the write flag 5 is H, the actual write signal 112, is outputted until actual writing execution to perform the writing, but when the write flag 5 is L, the write signal 12 goes down to L, so that the writing is not performed. Here, when a mode signal 10 is fixed at L, the value of DATA2 can freely be varied and the write control bit 1 is set to L to inhibit the necessary number of bytes from being written as necessary.