Provided are a disc guide mechanism 41 that is disposed on one end side of a slot 10A in a drive unit body 10 and guides an optical disc 1; and a disc diameter detecting mechanism 42 that is disposed on the other side of the slot 10A in the drive unit body 10 and retracts the disc guide mechanism 41 when the optical disc 1 inserted in the slot 10A is large and advances the optical disc 1 when the optical disc 1 is small. The disc guide mechanism 41 and the disc diameter detecting mechanism 42 which are respectively disposed on sides of the slot 10A can center the optical disc 1 in accordance with a diameter of the optical disc 1.