To magnetize rotor magnet materials of a plurality of kinds of outer diameters using a single magnetizer by arranging a yoke piece for forming a flux path from a yoke body to a rotor magnet material such that it can be adjusted with respect to the outer diameter of a rotor for fitting the inside surface and the rotor magnet material is subjected to the magnetizing field through the yoke piece.

A yoke piece 23 is secured, with respect to the outside diameter of a rotor 3 to be magnetized, at such position as the inside surface 25 is proximate to a rotor magnet material 5. The rotor 3 to be magnetized is then inserted into a rotor insertion hole 9 and arranged at a position where the rotor magnet material 5 on the outer circumferential part of the rotor 3 faces the yoke piece 23. Subsequently, a current is fed to magnetization coils 11a-11d to generate a magnetization field 29. In this regard, the yoke piece 23 serves as a flux path from a yoke body 7 to the rotor magnet material 5 and the magnetization field 29 is generated such that the field acts on the rotor magnet material 5 through the yoke piece 23. Consequently, the rotor magnet material 5 disposed in the magnetization field 29 is magnetized.