PURPOSE: To obtain a large displacement output at a second piston in a piezoelectric actuator which transmits displacement of a laminated piezoelectric body from a first piston to the second piston.

CONSTITUTION: A first to a fourth pistons 4, 5, 7 and 8 are moved back and forth interlockingly with telescopic displacement of a laminated piezoelectric body 6. As the fourth piston 8 makes a second oil chamber 12 communicate to a third oil chamber 14 in the middle of the forward movement, the second piston 5 is further moved forward. As the fourth piston 8 makes the second oil chamber 12 communicate to a reserve tank and the third piston 7 makes the third oil chamber 14 communicate to a reserve tank 16 in the middle of the backward movement, only the second piston 5 is kept in the forward movement state. Thus, by telescopically displacing the laminated piezoelectric body 6 for a plurality of times, a large output is obtained at the second piston 5.