This electrostatic actuator includes an electret film and a conductor layer formed on the electret film, and the conductor layer is so formed as to have a sectional shape reduced in width upward from the side closer to the electret film. The impact tool assembly is comprised of a solenoid driven reciprocating rod with adjustable travel and impact force. A length between a top of the first mountain portion and a bottom at the large diameter mounting member side is not more than a length between the inner peripheral position of the bottom and an end portion of an outer ring at the rotating shaft side. At the time of forward-direction operation, the first resonance circuit is formed by the capacitors in the surge voltage circuit and the inductor on the high voltage side.