PURPOSE: To secure such a bearing part that is excellent in quality and inexpensive in cost by forming a two-stepped recess in a lower bearing support part supporting a hollow shaft to which a stator is clamped, and fitting plural steel balls different in number and diameter in this two-stepped recess, respectively.

CONSTITUTION: A stator 2 is clamped to the center of a hollow shaft 1, and an E ring 3 is fitted in an outer diametral groove 15 at the upper side of this stator 2. This E ring 3 is set down as positioning and a bearing 4 is fitted in the hollow shaft 1. And, a peripheral part of the bearing 4 is fitted in the central part of an upper housing 6, while this upper housing 6 is solidly formed with a rotor 5 as one body. In addition, a boss 10 is erected in a lower part of the rotor 5, while a lower housing 9 is clamped to this boss 10. At this time, a two-stepped recess 8 is formed in the center of the lower housing 9, and simultaneously one large diametral steel ball 7 is housed in a lower step recess 11 and plural small diametral steel balls 7a in an upper step recess 12, respectively.