Abstract: A vendor ID is written to a system area of a write-once optical disk. When the write-once optical disk is loaded onto a write-once disk drive, a control CPU reads the vendor ID. The vendor ID is written into the header of software received through an interface unit. When the software is input to an SD circuit, the control CPU reads the vendor ID. The control CPU compares the vendor ID in the system area of the write-once optical disk with the vendor ID of the header of the software and checks whether or not the two IDs are identical. If the two IDs correspond to each other, the control CPU writes the software to the write-once optical disk.