To prevent the dropping of the driving torque of a rotary actuator due to the magnetic saturation of the actuator.

In a rotary actuator, a magnetic neck section 16 with a magnetic path having a small cross-sectional area is formed at a position which is shifted to the turning direction side from the facing position of the magnetic poles of rotor magnets 15, at the turning start point of the magnets 15 by a prescribed angle (for example, about 1/2 of the maximum turning angle) in a stator core 11, and the part of the core 11 on the turning direction side of the neck section 16 is formed is such a way that the cross-sectional area of its magnetic path suddenly becomes larger. In addition, the part on the opposite side of the neck section 16 is formed in such a way that the cross-sectional area of its magnetic path becomes gradually smaller as going toward the neck section 16. Consequently, a flat torque characteristic can be obtained, because the concentration of magnetic fluxes to the location having a smaller cross-sectional area of magnetic path (the thin-wall section of the magnetic neck section 16 on the side opposite to the turning direction) is eliminated, and the dropping of the driving torque of a rotary actuator by the magnetic saturation of the actuator near the turning end point of the magnets 15 is prevented.