PURPOSE: To obtain hollow structure by using PM type stepping where a hollow ring-shaped permanent magnet which has many poles magnetized is used as a rotor and a yoke part having magnetic poles opposite to it and a stator part having an exciting coil at its outer periphery are arranged.

CONSTITUTION: The ring-shaped permanent magnet 1 having the poles magnetized is used as the rotor, and a yoke 3 and a coil 2 are arranged at its periphery; and nothing is provided inside the magnet 1 and thus the hollow structure is formed. Further, it is preferable that the magnet 1 is subjected to radial anisotropy. Therefore, it is effective to use a rare earth element-cobalt resin bound type radial anisotropic permanent magnet, but it is composed basically of rare earth metal, iron, and boron to obtain the radial anisotropic permanent magnet having neither cracking nor chopping even when a sintering method is employed.