The present invention provides a slot-in type optical disk player which has a guide unit to guide an optical disk, inserted into an inlet, to a central portion of the inlet of the optical disk player, and a disk guide device to allow the optical disk player to play either of 80 mm and 120 mm optical disks. The disk guide device includes a chucking plate, a guide arm, a select arm, a push arm and a push lever. As such, the optical disk player of the present invention plays either of the 80 mm and 120 mm optical disks, so that the optical disk player is economical and practical. Furthermore, the optical disk player has the guide unit which is provided in a disk loading part.