To provide a high magnetic device of a servo motor by eliminating a reduction gear of conventional gears and cams, generating high torque without friction, and improving the chucking performance.

Sandwich structure of magnetic and nonmagnetic bodies is provided between a rotor A of a servo motor and an external coil, the polarity is subdivided, thus utilizing high magnetic force operating on the magnetic body, obtaining high torque characteristic, and at the same time securing chucking performance.