Electromagnetic clutch, electromagnetic clutch control device, and electromagnetic clutch control method

An electromagnetic clutch (100) provided with: an armature (4) in which two or more nonmagnetic sections (41, 42) of differing radii are provided and which is installed on a rotation shaft (LO); a rotor (1) in which three or more nonmagnetic sections (81-83) of differing radii that do not overlap with the nonmagnetic sections (41, 42) are provided on a friction plate (8) that faces the armature (4), and which rotates with respect to the rotation shaft (LO) by external force; a stator (2) equipped with an electromagnetic coil (3) for fixing the armature (4) to the rotor (1) by applying magnetic flux, which is generated by passage of an electric current, on the friction plate (8); and a control device (30) for the electromagnetic coil. The control device (30) is provided with a magnetomotive force-modifying circuit (10) for increasing, with an electric current passage start command to the electromagnetic coil (3), the magnetomotive force of the electromagnetic coil (3) above the magnetomotive force of normal electromagnetic clutch (100) operation and for returning the magnetomotive force of the electromagnetic coil (3) to the magnetomotive force of normal electromagnetic clutch (100) operation when the armature (4) is fixed to the rotor (1).