PURPOSE: To lessen the number of poles of a permanent magnet to obtain rotating torque more than a specific value by setting the number of poles of the permanent magnet to the extent of 6-24, and setting a space over 1,000mm in a magnetic coupling in which the permanent magnet and hysteresis material make the same rotation.

CONSTITUTION: A disc 2 is fixed around a motive shaft 1, a permanent magnet 3 is arranged on the end 2a of the disc 2 in the shape of a ring as shown in figure 2, and the total number of poles of N and S is 8. A specific space δis only separated from the permanent magnet 3 to fix the hysteresis material 8 to a disc 7 of an inverted shaft 6 in the shape of a ring. The permanent magnet 3 uses, for example, Sm-Ca rare earth magnet. The hysteresis material 8 is of Al-Ni-Co material, and a ring shaped one having 62mm in the inside diameter, 98mm in the outside diameter and 4.5mm in the thickness is used. As shown in the figure, when a distance from the permanent magnet is further than a certain extent, a magnetic couple with a less number of poles of the permanent magnet has high magnetic flux density and high rotating torque.