PURPOSE: To suppress settling and to rapidly stop a permanent magnet and then to miniaturize the device by engaging a brake member consisting of an elastic material with a rotor and preventing reverse rotation of the rotor.

CONSTITUTION: A coil 14 of a stepping motor 4 is electrified in order to rotate the rotor 2 and the permanent magnet 3 by 90 degrees. The rotor 2 is stopped by canceling electrification, but at this time, the rotation is slightly continued in the same direction by inertia of the rotor 2, and then afterward, rotation settling in the reverse direction is to be generated. However, the tip of a leaf spring 17 is engaged with toothed parts of a ratchet wheel 15 as well as the rotor 2 so that the permanent magnet 3 is quickly stopped. Thus, since the permanent magnet for impressing a bias magnetic field can quickly be stopped, it is not necessary to use a large size motor, and the miniaturization can be achieved.