PURPOSE: To simplify the construction and ensure opening and closing operation of contacts by making contact opening/closing action by the use of two resilient members, which deform in accordance with deformation of a piezo element and have a potential enlarging mechanism.

CONSTITUTION: Rigid members 2, 3 are fixed to the ends of a piezo element 1, and the distance between them varies when a voltage is impressed on the piezo element 1. Resilient members 6, 7 are fixed between these rigid members 2, 3. These resilient members 6, 7 have bends a, b and diverging arms 6a, 7a in the middle of the longitudinal direction, and the tips c, c of the diverging arms are contacted or separated according to displacement of the rigid members 2, 3 through the action of lever to provide contact opening/closing action. Because this construction is simple and free from friction in actions, there is little wear and sure contact action an be expected.