To impart pressurization to a bearing through a simple manufacturing process.

A spring member 51 is attached to the upper side of the bearing 16 of a shaft 13. In this case, the spring member 51 is formed by press working of an elastic metal and, with the shaft 13 inserted in a through-hole 52 formed in the center, the spring member is installed between a stator core assembly 61 and the bearing 16, thereby imparting pressurization of specific force to the inner race of the upper bearing 16. The stator core assembly 61 has a through-hole 62 formed along the center axis. The shaft 13 projecting from the upper part of the spring member 51 is press-fitted into the through-hole 62 of the stator core assembly 61. As a result, the stator core assembly 61 is fixed on a stationary drum 12 through the shaft 13.