NOVELTY - The device (150) has a low speed magnet rotor (120) including a magnet array (122) to be magnetized along a circumferential direction. An inductor rotor (130) allows magnetic flux of a magnet array (112) of a high speed magnet rotor (110) to pass through a magnetic body portion (126a) of the low speed magnet rotor, where the high and low speed magnet rotors and the inductor rotor are concentrically arranged, and the magnet array of the low speed magnet rotor is formed such that homopolar surfaces of neighboring magnets (124a, 124b) face each other along the circumferential direction.    USE - Non-contact power transmission device for use in a wind turbine generator, an air blowing device and an in-wheel motor (claimed), for a vehicle.    ADVANTAGE - The device allows closed magnetic flux to be effectively induced to the magnetic body portion by the magnet array of the low speed magnet rotor to reduce leakage magnetic flux of the high speed magnet rotor, the low speed magnet rotor and the inductor rotor and homopolar surfaces of neighboring magnets of the magnet array of the low speed magnet rotor to face each other along the circumferential direction such that the magnetic fluxes which pass through the low speed magnet rotor pass in an aligned state, magnetic coupling strengths of the rotors can be increased and outer periphery portion side can make a yoke of the inductor rotor to be thinner and an outer shape of the inductor rotor can be made smaller to achieve greater allowable torque in top and back surfaces of the low speed magnet rotor, while the device is small to achieve wide range of an acceleration and deceleration ratio.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of a closed magnetic field formed in a power transmission device.    Magnetic fluxes of magnetic array of rotors (pie-120, pie-122, pie-124a)    High speed magnet rotor (110)    Magnet array of high speed rotor (112)    Low speed magnet rotor (120)    Magnet array of low speed rotor (122)    Neighboring magnets (124a, 124b)    Magnetic body portions (126a, 126b)    Inductor rotor (130)    Non-contact power transmission device (150)