The library device comprises a cartridge load/unload mechanism (5, 18, 288) for loading a recording medium cartridge (30) into the library device and unloading the cartridge from the library device; a cell unit (3) having a plurality of cells each for containing the cartridge; a drive unit (6) for reading and writing data from and to a recording medium contained in the cartridge, the drive unit having ejecting means for ejecting the cartridge from the drive unit; an accessor (2) for carrying the cartridge between the cartridge load/unload mechanism, the cell unit, and the drive unit; and a stopper means (250) provided in opposition of a cartridge inlet/outlet end of the drive unit, for inhibiting excess ejection of the cartridge from the drive unit, wherein in inserting the cartridge into the drive unit by means of the accessor, the stopper means is lowered to allow insertion of the cartridge into the drive unit, whereas in ejecting the cartridge from the drive unit, the stopper means comes into collision with the cartridge to stop the cartridge.