An AC servo motor in which annular polar anisotropic magnets, formed by splitting an anisotropic magnet into two or more portions in an axial line direction, are used in a rotor. The magnetic poles of the split annular polar anisotropic magnets are disposed so as to be shifted by a predetermined angle &thgr;′ which is greater than a skew angle &thgr; determined based on the number of torque ripples per rotation of the rotor determined by the number of magnetic poles and the number of slots in a stator-side iron core. The predetermined angle &thgr;′ is the angle obtained after adding to the skew angle &thgr; a value which takes into consideration magnetic interference between the magnets. The invention provides an AC servomotor which can be controlled with high precision as a result of reducing cogging torque generated between the magnet and the stator-side iron core.