To avoid dislocation or slant of the bearing center of bearing holes due to assembling tolerance between members by forming the bearing holes after assembling a bearing housing out of housing constituting members.

A bearing housing 12 is assembled out of a cylindrical housing constituting member 12a and disc-like housing constituting members 12a. The stator 14a of an electric motor 14 is assembled inside the cylindrical housing constituting member 12a, and the disc-like housing constituting members 12a are assembled on the upper and lower opening ends of the cylindrical housing constituting member 12a. When the bearing housing 12 is assembled, the stator 14a is assembled in the bearing housing 12. Hereby, dislocation or slant of the bearing center of bearing holes 11a due to working tolerance between the bearing holes 11a can be appropriately avoided.