A fixing structure fixes the position of a spindle motor against a traverse chassis in the direction of the movement of an optical pickup (first direction), and can be adjusted in the direction perpendicular thereto (second direction). In the bottom surface of the spindle motor: an elongated reference hole, the longest dimension of which extends in the radial direction, centered on a main shaft; and three screw holes circumferentially spaced, centered on the main shaft. A traverse chassis includes a protrusion engaged within the reference hole; and elongated through holes elongated in the second direction at positions corresponding to those of the screw holes. The cross-sectional width A of the protrusion in the first direction is approximately the same as the width of the reference hole, while the cross-sectional width B in the second direction is smaller than the cross-sectional width A in the first direction.