PURPOSE: To confirm the loss of a back-up function and to improve the check reliability of an IC card by switching an external power supply to a battery serving as an internal power supply before execution of the verifying check.

CONSTITUTION: The power is supplied to a RAM 6 from a power supply 21 via a switch circuit 24, the supply terminal 22P and 22N, and the power terminals 1P and 1N with an IC card 10 connected to a read/write device 20. An OFF pulse is applied to the circuit 24 from the device 20 via a BUS after the data are written into the RAM 6 of the card 10. Then the device 20 reads the data out of the RAM 6 for execution of the verifying check. The data stored in the RAM 6 are erased when the circuit 24 is turned off even when the back-up function of a battery 5 is lost owing to the OFF state of the circuit 24. Then the abnormality of a power circuit is decided since no data is read out in a verifying check state.