Rotor structure

1. A rotor comprising:

a magnet having a circular cylinder shape and having a hole formed through its axial center, wherein the hole has in axial cross section a regular polygonal shape having flat portions and angle portions, and a recess having a truncated cone shape is disposed at an axial end of the magnet such that the recess has its maximum diameter portion located at the axial end and has its minimum diameter portion communicating with the hole;

a shaft fitted in the hole of the magnet, wherein an outer circumference of the shaft makes contact with the flat portions of the hole of the magnet thereby forming a plurality of gaps between the outer circumference of the shaft and the angle portions of the hole of the magnet, and adhesive is filled in the gaps,

wherein a volume calculated by deducting a volume of a portion of the shaft residing in the recess from a gross capacity of the recess is substantially equal to a total volume of the plurality of gaps; and,

wherein the angle portions of the polygonal shape of the hole of the magnet are rounded, and a distance from the outer circumference of the shaft to the angle portion is 0.05 mm or smaller.

2. A rotor according to claim 1 , wherein a wall inclination angle of the recess with respect to an axis of the magnet ranges from 30 to 60 degrees.