PURPOSE: To prevent obstacles such as dielectric breakdown and so on by alternately changing a code of voltage to be applied pulsatively between electrodes holding the electroviscous fluid.

CONSTITUTION: An actuator is constituted by using the electroviscous fluid which is the liquid to disperse fine grains causing a dielectric polarization by impressed external field into the electric insulating oil. The actuator actuates the electroviscous fluid by impressing the voltage between electrodes holding said fluid. At this time, as impressed voltage, it is so constituted that the voltage changing a code alternately is pulsatively impressed. According to the constitution, the settling due to the charge of fine grains in the electoviscous fluid can be prevented.