An electric motor having a speed change function is configured to differentiate a rotational speed of a rotor from a rotational speed of an output shaft outputting a torque transmitted from the rotor. The electric motor includes: a stator coil arranged on an inner circumferential face of a cylindrical outer case; a cylindrical rotor which is arranged in an inner circumferential side of the stator coil, and which is adapted to generate a torque by receiving a magnetic force generated by the stator coil; and a continuously variable transmission mechanism, which is arranged in an inner circumferential side of the rotor, and which is adapted to continuously vary a ratio between a rotational speed of an input member connected with the rotor, and a rotational speed of an output member connected with the output shaft and rotated by the torque from the input member.