Prior to the loading of a main program, the rotation speed of a disk provided in a hard disk drive is increased to a common rotation speed adapting to all types of hard disk drive. At the common rotation speed and a common recording density, a main program is read from a system area in the disk where the main program is recorded. The main program is written to a RAM provided in a hard disk controller. After control processing of the hard disk drive is handed over to the main program, the rotation speed of the disk is increased to a proper rotation speed for a device. This allows main programs to be loaded in a common way from disks provided in respective hard disk drives independent of the type thereof.