The present invention writes intrinsic information such as the current time, etc. to both a memory and a storage medium when an exchangeable storage medium inserted in a drive device is mounted to a system. If the storage medium is removed from the drive device when the storage medium is being I/O accessed, then the execution of the present and the succeeding I/O requests is suspended. Then, if a storage medium is inserted in the drive device, then it is checked whether or not the intrinsic information stored in the memory has been written to the storage medium. Only when the information has been written to the storage medium, the suspended request for the storage medium is resumed. Accordingly, even if a storage medium has been erroneously removed from the drive device, all I/O requests are surely executed without being lost if the erroneously removed medium is inserted again. Furthermore, the data in a replacing storage medium won't be erroneously lost, either. The stop of power supply for a drive device is permitted only when a storage medium is not mounted to a system. Therefore, all I/O requests for the storage medium have been executed, and the data in another storage medium are not lost when power supply is resumed with another storage medium inserted during the suspension of the electric power supply.