To cope with accidental impact inflicted upon an optical pickup unit when the unit moves beyond a prescribed range, resin support members integrally formed with the chassis of a traverse unit and supporting the ends of main and sub guide rails at a prescribed distance are provided on the chassis, so that the impact caused by the collision against the support members for the guide rails is absorbed. Buffer members integrally formed with the support members adjacent to the center and upright perpendicularly to the chassis are provided at least between the support members for the main guide rail, so that the impact upon the optical pickup unit is absorbed.