An optical disk includes a standard area of a standard recording density provided on an inner peripheral side and a high density area of a higher recording density provided on an outer peripheral side. In each of the standard area and the high density area, a program area is provided so that an independent program can be recorded in each program area. In, one aspect of the invention, an optical disk includes, from the inner periphery to the outer periphery of the disk, a ROM area for read-only purpsoe, a RAM area in which information can be rewritten and a WO area in which information can be written only once.