PURPOSE: To take out a tape cartridge by a transport mechanism without a cartridge push-in mechanism becomes a stopper of the tape cartridge in the cartridge throw-in device of a magnetic tape device with an automatic storage box.

CONSTITUTION: In a cartridge throw-in device 101, when a transport mechanism takes out a tape cartridge 3 from a cartridge take-out port 7, a movable stopper mechanism 5 is provided at the location where the tape cartridge 3 is prevented to move back in the direction towards a cartridge insertion port 6. The mechanism 5 has a movable section which is installed and being freely turnable with respect to the hinge fixed on the cartridge throw-in device 101. This movable section springs up when the cartridge 3 moves toward the cartridge take-out port and when the cartridge 3 passes, the section goes back to an original position to prevent the cartridge having a move back motion.