DATA CARTRIDGE CADDY EXISTENCE SYSTEM

PROBLEM TO BE SOLVED: To enable rapid and efficient retrieval of a caddy and a data cartridge in an auto-changer by equipping an optical sensor. SOLUTION: Caddy guide upper plates are provided with optical sensors respectively, and at the time of fitting a caddy guide reference sleeve 500 to each upper plate, the caddy guide reference sleeve is extended to each optical sensor through a hole 508 provided corresponding to the optical senpor. When the caddy 300 is introduced into a storage rack, the optical sensor is operated by a light shielding flag 326 provided on the upper plate of the caddy 300 to send an electronic signal to a controller of a pickuer. Consequently, the existence of a caddy 300 of data cartridges is discriminated, and then a position of nonexistence of a data cartridge in the caddy is skipped without performing an operation of removing this data cartridge. Instead of the optical sensor, a reflecting sensor, a magnetic sensor or a microswitch can also be used.