In a disc changer provided with a driving force transmission mechanism using a crank arm, the size of the crank arm is reduced as much as possible and the smooth movement of the tray is realized. The crank arm (7) is rotated by a driving force of a drive motor (5). The crank arm (7) has a distal end (71a) connected to a guide groove (100) formed at the tray (1). When the crank arm (7) rotates, the distal end (71a) moves along the guide groove (100). When the distal end moves through a left end curve (120) or a right end curve (130) at opposite ends of the guide groove (100), the rotational force of the crank arm (7) is transmitted to the tray (1), whereby the tray (1) performs open/close movement. The guide groove (100) has a bow shape made up of an arcuate intermediate curve (110), and the left end curve (120) and the right end curve (130) which are curved opposite to the intermediate curve (110), so that the force to be transmitted to the tray (1) changes continuously. Therefore, the smooth movement of the tray (1) and the size reduction of the crank arm (7) are possible.