To provide a rotor with mounting structure of a rotor core and a rotor shaft in a motor, in which propagation of oscillation and noises is prevented.

A rotor core 2 has an inserting hole 2a at its center for inserting a rotor shaft 3. The inserting hole 2a has opposite U-shaped grooves 2b along an inner wall in an axial direction, while the rotor shaft 3 has a flat part 3a opposite to the groove 2b at an outer surrounding part thereof in the axial direction. In addition, a cushion member 5 made of rubber with hardness of 40° to 60° is applied and formed between the rotor core 2 and the rotor shaft 3 when the rotor core 2 is mounted on the rotor shaft 3.