PURPOSE: To suppress magnetomotive force loss and to improve the performance of a motor by forming a tapered through hole in a disc-like rotor, and adapting a pair of tapered permanent magnet pieces coincident with the shape of the hole.

CONSTITUTION: Tapered through holes 18a are formed at both sides near the peripheral edge of a disc 18 supported to a rotational shaft 10, and a pair of permanent magnet pieces 20a, 20b are inserted from both faces of a rotor 18 into the holes 18a. The pieces 20a, 20b have a shape coincident with the tapered shape of the hole 18a, and the holes 18a are completely blocked in a state that the pieces 20a, 20b are inserted. A ferromagnetic material is not interposed between the pieces 20a and 10b. As a result, the pieces 20a, 20b are sucked to each other to be integrally secured, held by the tapered faces of the holes 18a to prevent them from dropping from the holes 18a. Thus, loss of magnetomotive force can be suppressed.