A linear motor is movably disposed in a disc unit internally provided with a cartidge holder for loading and ejecting a disc cartridge and is securely locked by a locking mechanism at the time of ejection of the cartridge. The locking mechanism comprises a first locking member extending downwards from the cartridge holder and a second locking member securely mounted on the linear motor. When the disc cartridge is ejected by the cartridge holder, the first locking member is brought into contact with the second locking member to move the linear motor toward a location at which the linear motor is securely locked.