A bucket is so supported by a pair of supporters that it can move up and down, through vertical slits formed in the supporters and pins formed on the bucket and entering the vertical slits. A guide member can reciprocate horizontally, along one of the supporters. The guide member has slanted slits into which the pins on the bucket are individually fitted. When a cartridge is horziontally inserted into the bucket, a slider moves forward in conjunction with the cartridge, thereby rocking the interlocking body retaining the guide member, to disengage the guide member from the interlocking body. The guide member is moved in the cartridge retreating direction by a tension spring, and the bucket is lowered by the joint action of the slanted slits, the vertical slits and the pins. Thus, a magnetic disk engages with the shaft of a motor. If an ejecting lever is pushed in, the guide member moves in the cartridge insertion direction and the bucket is raised by the action of the slanted slits, etc. Thus, the magnetic disk is disengaged from the motor shaft. At the same time, a stopper is also raised, so that the cartridge is retained by the stopper. If the ejecting lever is released, the stopper is then lowered, so that the cartridge is pushed out of the bucket by the slider.