A difference is arisen in the electric potential of the electrode layer between a fixed end portion and a displacement end portion of an actuator. A girdle is arranged with a close fit round the joined casing parts. The first, second and third SOI regions are coplanar. The wire rod is wound around a bobbin so as to have a solenoid shape. Then, the test pattern is input to the path under test and the resultant output value is compared to the expected value.