PURPOSE: To prevent the destruction of identifying information stored in an identifying register and to protect this information, by inhibiting writing actions in the identifying register while a memory card is kept under a write protection state.

CONSTITUTION: When the write protection state is secured with a WP switch 11 connected to a power supply VCC, the input terminal of an inverter gate 17 is set at an H level with the write protection signal set at an L level. Thus the output of an AND gate 13 is also set at the L level to inhibit the information to be written in a memory 1. Then a port address indicating write of the identifying information and the write signal are applied to a control circuit 9. Thus an identifying register load signal is set at the H level and given to the other input terminal of an AND gate 15. Even under such conditions, the input terminal at one side of the gate 15 is set at the L level since the write protection signal is kept at the L level. Then it is inhibited to write the identifying information in an identifying register 5.