In a disk identifying device, when a slanting reflecting face is irradiated with light emitted from a light emitting element while a rotary tray is rotating, most of the light reflected from the slanting reflecting face is not incident on a light receiving element, whereas when a flat reflecting face is irradiated with the light emitted from the light emitting element, most of the reflected light is incident on the light receiving element. Since the receiving element receives the reflected light in a pattern corresponding to an assigned number of a pertinent disk placing portion, the rotary position of the rotary tray is detected. Where a disk detecting hole is irradiated with the light emitted from the light emitting element, the presence or absence of a disk on the pertinent disk placing portion is detected by the presence or absence of the reflected light received by the light receiving element.