To easily regulate the frequency of vibration intrinsic to a driving part by providing a driving means for reciprocating driving a movable member in an axial direction with respect to a fixing side member, and providing a capacity regulating means for changing a capacity of a compression chamber when the movable side member is positioned on a neutral point of an axial direction with respect to the fixing side member.

When a.c. flows through a coil 16, a piston 7 attached through a capacity regulating mechanism 30 on a bottom of a coil bobbin 12 whose tip part is provided with a coil 16 is reciprocatingly driven. Since the piston 7 is vibrated with synthetic spring constant of a gas spring and a plate spring 8 and the intrinsic frequency of vibration found out from a mass of a movable part, a capacity of a compression chamber 4 is periodically changed, and supplying and recovering of compressed gas is repeated through a gas passage 2. In the case where the intrinsic frequency of vibration of the piston 7 is regulated, a depth for inserting a regulating rod 31 to a sleeve 32 in a capacity regulating mechanism 30 is changed, and thereby, the capacity of the compression chamber 4 is changed when the piston 7 is positioned on the neutral point.