An actuator for rotating (or moving) a rotor (or a moving member) according to the current flowing through an electromagnetic coil. Magnetic energy of magnetomotive force induced in the electromagnetic coil when energized is stored in an air gap and a sub-air gap provided in a magnetic path. The rotor (or the moving member) comes to rest at a position where the stored magnetic energy becomes the smallest. The stored magnetic energy serves as a source of counterforce and functions in the same way as a spring.