To obtain a motor excellent in rotational performance by employing a bearing unit as is where, components are preassembled in a motor on the manufacturer side.

An inner circumferential rolling groove 2a is made in the outer circumference at the large diameter part of a two stage shaft 1 having a large diameter part 1a and a small diameter part 1b. Balls 4 are filled in the gap between the inner circumferential rolling groove and an outer circumferential rolling groove 2b made in the inner circumferential surface of an outer ring 3 on the larger diameter part while balls 6 are filled between inner and outer rings 5a, 5b thus constituting a ball bearing 5. A tubular spacer 7 provided, at the opposite end parts thereof, with small diameter parts 7a, 7b being fitted, respectively, in the outer ring 3 at the large diameter part and the outer ring 5b of ball bearing 5 is interposed between both outer rings 3, 5b and the inner ring 5a of the ball bearing is fitted over the small diameter part 1b of two stage shaft thus constituting a bearing unit. The bearing unit is fitted with the central hub 11 of rotor 10 of a motor.