Patent ID: 7196437

Claim:
A contraction type actuator comprising: a magnetostrictive rod composed of a magnetostrictive member, an end of the magnetostrictive rod being fixed; a bias magnet for applying a bias magnetic field to the magnetostrictive rod; and a magnet coil for applying a magnetic field in a direction that cancels the bias magnetic field, the magnetostrictive rod flexibly expanding and contracting by controlling strength of the magnetic field applied by the magnet coil, wherein the bias magnet comprises: a first bias magnet in the shape of a cylinder, the first bias magnet being coaxially disposed around the magnetostrictive rod; a second bias magnet disposed in an inner space of the first bias magnet, attached in an axial direction of the magnetostrictive rod and separated from the rod, the second bias magnet is magnetized axially so that its magnetic field adds to or draws a part of the first bias magnetic field into the space inside the cylindrical first bias magnet; and a total axial length of the magnetostrictive rod and the second bias magnet is shorter than an axial length of the first bias magnet.