Whether an initial command outputted from a host is `CMD1` or `CMD55+CMD41` is detected with an initial command detection portion 8, and the result of detection is set in an SD/MMC register 13. Reset process for hardware and that for firmware are carried out based on the result of detection set in the SD/MMC register 13. Thereafter, a microcomputer 7 sets data indicating in which mode, MultiMedia Card mode or SD mode, the firmware reset process was carried out, in a F/W process SD/MMC register 14. A H/W-F/W mode comparison circuit 15 compares data in the SD/MMC register 13 with data in the F/W process SD/MMC register 14. If these data agree with each other, busy state is released, and command wait state is established. If they disagree with each other, a disagreement occurrence detection signal is outputted to the microcomputer 7, and power-on reset processing is performed again.