PURPOSE: To prevent the start failure against the fault of an external storage whose start is designated by checking the fault information on the external storage at rise and selecting an external storage to be started.

CONSTITUTION: A magnetic disk device fault information reading means 2 is started and reads the 2nd magnetic disk device fault information 42 and the 1st magnetic disk fault information 52 out of a 1st magnetic disk device 4 and a 2nd magnetic disk device 5 respectively. Then the information 52 is judged in a 1st magnetic disk device application judgement step of a magnetic disk device reading means 1. If an available state of the information 52 is judged, the information is read out of the device 4 in a 1st magnetic disk device reading step. Thus an external storage is surely started.