Abstract: An actuator having a simple configuration requiring no high dimensional accuracy, high in positioning accuracy and low in cost, and a head-positioning mechanism using the actuator are disclosed. An actuator according to a first application comprises a shear-type piezoelectric element of predetermined thickness and an opposed electrode formed on two electrodes in spaced relationship on a base member. The opposed electrode is displaced in accordance with the direction of polarization of the shear-type piezoelectric element upon applying a voltage between the two electrodes. The opposed electrode thus constitutes an operating section of the actuator. An actuator according to a second application comprises a movable member arranged on a drive member including a shear-type piezoelectric element on a base member. The drive member includes a plurality of layers of piezoelectric elements polarized in alternately opposite directions perpendicular to the thickness of the devices.