A head positioner has a configuration employing a dual-stage actuator method, wherein positioning control is performed for a write/read according to cooperative operations of a coarse actuator and a fine actuator, and the fine actuator is configured using a piezoelectric device. A positioning control unit for controlling the coarse actuator and the fine actuator is configured to include a coarse control system including a coarse drive unit for driving the coarse actuator and coarse control unit for controlling the coarse drive unit, a fine control system including a fine drive unit for driving the fine actuator and a fine control unit for controlling the fine drive unit. In addition, a driving-signal limiting unit is provided. The piezoelectric device is prone to property deterioration because of erosion due to an electrochemical reaction. The driving-signal limiting unit limits the level of a fine control signal fed from the fine control unit to the fine drive unit to be below a threshold at which property deterioration of the piezoelectric device is caused by an electrochemical reaction. Further, as a median-value signal, a relative displacement signal ranked in the center of a plurality of relative displacement signals sent from a plurality of the individual fine actuators is selected. The coarse actuator is controlled according to the selected median-value signal.