For example, a rotor 1 having eight magnetic poles, has 12 slots, in combination with stator 2 having a ripple component of permeance to generate cogging torque on the approximate sine wave in the same number as the number of pole rotor 1, by pressurizing the outer periphery of the stator 2 on the inner side in pressurizer 3 disposed at a position of the predetermined four portions, which were to cancel the number of poles of the same number of cogging torque ripple component rotor 1.