The vibration and noise excited by the electromagnetic exciting force in the radial direction of an electric motor are suppressed.In an electric motor 100, a rotor 1 is divided into four rotor pieces 3, 4, 5, and 6 for an axial length of 2L of one group of the rotor core, and for example, the four rotor pieces 3, 4, 5, and 6 are ideally 0.29L, 0.71L, 0.71L, and 0.29L in axial length in the axial direction, and permanent magnets 2 of the rotor pieces 3, 4, 5, and 6 are arranged in the circumferential direction so that the phase differences of the electrical angle are 0, .pi., 0, and .pi.. Further, when an effect is obtained even if the ideal axial length is changed, the tolerance of the aforementioned axial length is .+-.0.1L.