PURPOSE: To provide the head actuator which is relatively small in power consumption even for the same displacement and makes a superior step response as compared with a conventional actuator although the side is small.

CONSTITUTION: This head actuator optionally moves an objective lens 17 in the direction vertical to the surface of a discoid medium 27 and is provided with one laminated piezoelectric element 13 and a base and a cap 16 which are made of rigid body members and couple with both the ends of the element 13. The objective lens and a housing 18 are coupled by an external arm 14, an intermediate arm 15, and a flexible beam 19 through flexible hinges 21 and 25, and a voltage is applied to the laminated piezoelectric element 13 to finely control the position of the objective lens 17 on the surface of the discoid medium 27.