PURPOSE: To keep the distance between an optical card and an objective lens always constant by providing a projection to a hold member of an objective lens and using a bias means so as to contact the projection onto the optical card through the biased hold member.

CONSTITUTION: A prescribed current flows to a coil 14 to move a head 3 widely along a shaft 2 or moved at a minute range to apply tracking control. A permanent magnet 16 is provided to the head 3 at a part opposed to a permanent magnet 15b and the ball 6 is in contact with the optical card 1 in the head 3 by the repulsive force. Since the head 3 is biased through the repulsive force between the permanent magnets 15b, 16 in a direction in contact with the optical card 1, the ball 6 provided to the head 3 is in effective contact onto the optical card 1. Since the ball 6 is rotated and in point contact with the optical card 1, the friction is less. Thus, the distance between the objective lens 9 and the optical card 1 is kept always constant.