To prevent the leakage of lubricant fluid from a bearing mechanism having high rotating accuracy.

In the bearing mechanism 3 for a motor part 2, a sleeve 32 into which a shaft 31 is inserted is fixed into a sleeve holding part 33 with its outer peripheral face thrust by the inner peripheral face of the sleeve holding part 33 formed of a resin. An circular member 35 is fixed into the sleeve holding part 33 in the state of abutting on the upper face of the sleeve 32. The shaft 31 has a tapered portion, and the diameter of a gap between the tapered portion and the circular member 35 gradually increases as going upward where a tapered seal is formed to retain oil. Thus, the deformation of the inner peripheral face of the sleeve 32 and the leakage of the oil from the bearing mechanism 3 are prevented to improve the reliability of the motor part 2 having high rotating accuracy.