As methods for preventing the overlap of the idle seek times of the respective disks 37 1 to 37 n, there are a method of shifting the time (spin-up processing time) of issuance of a spin-up command to each of the disks 37 1 to 37 n and a method of providing dummy access (a dummy read command) to each of the disks 37 1 to 37 n from the FC control logic and power source monitor circuit 77 1.