To effectively suppress internal vibration by providing a self- compensating balancer so as to place a center of gravity of a spindle motor around its rotary shaft oppositely to the center of gravity of a disk by a centrifugal force during the rotation of the disk.

A turntable 200 is fixed on a rotary shaft 130 and rotated by a spindle motor 100 and a disk 1 and a clamper 300 are also rotated together. A self-compensating balancer 400 for suppressing the eccentricity of the disk by using a rotational center and the eccentric mass of the disk 1 is provided. The balancer 400 is provided in one selected from the rotary shaft 130 rotated by a rotating force from the motor 100 and the clamper 300. The balancer 400 includes a number of rigid bodies or fluids freely moved away from a rotational center by a centrifugal force during rotation. By the movements of the rigid bodies, the rotation of the shaft 130 caused by the disk eccentric mass is roughly suppressed and, by the fluids, the shaft 130 is finely suppressed.