Abstract: A disk arrangement is formed for a key by installing a plurality of disks, where each disk is either penetrable or non-penetrable by infrared light, into a plurality of through holes in the key. Selection of different types of disk for installation results in different disk arrangements for the key and the key is specified by its own disk arrangement. A lock is set to identify the key by detecting and storing the disk arrangement of the key by transmitting and receiving infrared light through the disks. The detected disk arrangement is stored in a memory device of the lock.