A positioning control device (14) executes disturbance observer control having a disturbance suppression function, wherein changes of control characteristics are prevented even if the disturbance frequency (ω) is suppressed. When a control value of an actuator (1) is computed using estimated gains of the actuator and estimated gains of disturbance according to an estimated position error (e[k]) by disturbance observer control including a model of the actuator and model of the disturbance, the disturbance frequency is estimated according to the estimated position error, and the estimated gains of the actuator and the estimated gains of the disturbance, corresponding to the disturbance frequency, are changed. Therefore appropriate observer control according to the disturbance frequency can be implemented.