An IPM (Interior Permanent Magnet) motor system is provided with an IPM motor provided with a stator having slots and a rotor having poles, and a control unit which controls the rotor to the stator. An estimation precision of an initial angle position of the rotor to the stator is selected such that it is substantially the same as an angle unit precision of stable positions of the rotor to the stator which is based on a combination of the number of poles and the number of slots. In this way, the cheap IPM motor system with a high drive efficiency and a control method of the IPM motor system are provided.
