PURPOSE: To prevent the consumption of a battery and the loss of data listed up in a memory by prohibiting the outflow of current from a backup battery in a card to a main body side when the memory card is put into a state of power source off on the main body side while the card is held mounted in the device body.

CONSTITUTION: A diode D2 is connected between a connecting pin p1 connected with the positive pole of a power supply voltage Vcc2 on the device body 21 side and a power source line L1 of the memory card 1 at the time of mounting the memory card 1 in the body 21. Inverter circuits 5a, 5b are connected in series between a chip enable terminal bar CE of a RAM 2 and a connecting pin p5 inputted with a chip select signal bar CE and the other end of a pull-up resistor R1 connected to the input terminal of the inverter circuit 5a is connected to the connecting pin p1 described above. As a result, the current outflow from the memory card 1 side to the device body 21 side is completely prevented.