PURPOSE: To simplify a servo mechanism and a control circuit by driving a mobile body in a medium plane direction and an orthogonal direction by a magnetic circuit and plural coils.

CONSTITUTION: When a focusing coil 108 is energized, the mobile body 103 can be moved since a slider 101 is held with a guide shaft 104 and an elastic wire 102 is expanded/shrunk. The centroid of the mobile body 013 including a loading material exists on the line of a driving point 1O8a, therefore, no angular moment is generated when it is driven. When the trace control of an objective lens 6 is performed along the track groove of an optical disk 10, the coil 108 is energized so as to trace the waviness of the groove, and the mobile body 103 is moved in fine quantity in a direction of (α). When the objective lens is moved tracing the fluctuation of a high frequency component, the mobile body 103 is moved mainly, and both the mobile body 103 and the slider 101 are moved integrally for the fluctuation of a low frequency component. Since the mass of the mobile body 103, etc., is small, a sufficient control band can be obtained. In such a way, the servo mechanism and the control circuit can be simplified.