To provide a machine tool equipped with an electric motor capable of securing a prescribed output in a wide speed range.

An electric motor for use has a stator having primary winding, and a rotor having a magnet for a field and a shaft. The magnet for the field has a first magnet for the field, in which magnetic poles different in polarity are disposed sequentially in the rotational direction, and a second magnet for the field, in which the magnetic poles different in polarity are disposed sequentially in the rotational direction. The electric motor has a mechanism which makes one of the first and second magnets displaced in the axial direction and the rotational direction with respect to the other one of them, so as to change a synthetic magnetic field brought about by the first and second magnets.