To provide a rotor which improves response of a motor irrespective of a position of a magnetic polarity.

The rotor 10 includes a rotating shaft 11, a rotor back yoke 12 fixed so that it may integrally rotate around the rotating shaft, and a permanent magnet 13 which is stuck to the outer peripheral face of the rotor back yoke. The rotor back yoke 12 includes a hollow portion 12b in an axial intermediate portion, at such a portion as excluding an outer periphery 12c in contact with the permanent magnet 13. A magnetic path width W1 of the outer periphery 12c is constituted to have a dimension which does not cause saturation of magnetic flux.