PURPOSE: To improve efficiency in a mechanism which is used for an actuator in which a magnetostrictive material and the like are used, liquid is used as displacement transmitting medium between a displacement generating material and an operated body, and for transmitting to the operated body the displace ment of the displacement generating material by Pascal's principle after enlarg ing it.

CONSTITUTION: Liquid 9 which in used as a displacement transmitting medium is filled in a container 21 which consists of bellows 23, 24 and the like which are easily to expand and contract in displacement transmitting direction and being difficult to expand and contract in a direction at right angles to displacement transmitting direction. Since a sliding seal is not used, loss is reduced.