An elastic restriction section (15g), formed in a substantially cylindrical configuration and having the vertical axis is provided to protrude on one side of a rear end section of a chassis (15) formed of a synthetic resin. The chassis constitutes a case body for housing a main body that performs processing of reading or recording of an optical disk. The elastic restriction section (15g) is divided into three elastic members that are elastically deformable into a diameter-reduced state, and provided to protrude at a position substantially diagonally opposite to an engagement position of a movement gear (63) of an open/close drive unit (60), the open/close drive unit (60) advancing/retreating a disk tray (50) carrying the optical disk. In the disk tray (50), an engaging recess (51e) is provided to be engaged with the elastic restriction section (15g) at a home position. Even when vibration is applied to the disk tray (50) while the optical disk is processed, the vibration is absorbed by the elastic restriction section (15g) that engages with the engaging recess (51e) to apply restoring force in different directions, thereby suppressing noise.