An inner rotor multiplex multiphase winding AC motor comprising: an armature iron core provided with a plurality of teeth and a plurality of slots; an armature winding electrically divided into two or more winding groups (100, 200) of multiphase windings that are wound around the teeth and are contained in the slots; a plurality of motor driving apparatuses (10, 11) independently connected with the two or more winding groups (100, 200) of multiphase windings; and a magnetic-field-pole iron core provided with a plurality of magnetic-field poles arranged in such a way as to face the armature iron core through an air gap, wherein the magnetic-field-pole iron core is provided with a plurality of magnetic resistance elements for impeding a magnetic-flux flow in the circumferential direction thereof, wherein the magnetic resistance element is configured with a slit (13, 14, 19, 22, 23) formed in the magnetic-field-pole iron core, wherein one or more of the magnetic resistance elements are arranged every 180° electric angle, wherein the slit (13, 14, 19, 22, 23) is disposed ranging from the surface, of the magnetic-field-pole iron core, that faces the armature iron core to the inside of the magnetic-field-pole iron core, characterized in that the magnetic-field-pole iron core is formed from two or more kinds of thin laminated plates (A, B) having different shapes, wherein the magnetic resistance element is provided in at least one kind of the thin plates (A, B), wherein the two or more kinds of thin plates (A, B) are stacked on top of each other so as to vary the shape of the slit (13, 14, 19, 22, 23), thereby adjusting the magnetic resistance, and wherein letting h1 and h2 denote the width of the slit (13, 14, 19, 22, 23) in the circumferential direction of the magnetic-field-pole iron core and the depth of the slit (13, 14, 19, 22, 23) in the radial-direction thereof, respectively, the slit (13, 14, 19, 22, 23) is configured in such a way that h2/h1 is larger than 1.0, wherein a minimum slit pitch θ given in electric angle is θ = 180°, or θ = 60°, or θ = 35°, or θ = 30°, or θ = 25°, or θ = 20°. an armature iron core provided with a plurality of teeth and a plurality of slots; an armature winding electrically divided into two or more winding groups (100, 200) of multiphase windings that are wound around the teeth and are contained in the slots; a plurality of motor driving apparatuses (10, 11) independently connected with the two or more winding groups (100, 200) of multiphase windings; and a magnetic-field-pole iron core provided with a plurality of magnetic-field poles arranged in such a way as to face the armature iron core through an air gap, wherein the magnetic-field-pole iron core is provided with a plurality of magnetic resistance elements for impeding a magnetic-flux flow in the circumferential direction thereof, wherein the magnetic resistance element is configured with a slit (13, 14, 19, 22, 23) formed in the magnetic-field-pole iron core, wherein one or more of the magnetic resistance elements are arranged every 180° electric angle, wherein the slit (13, 14, 19, 22, 23) is disposed ranging from the surface, of the magnetic-field-pole iron core, that faces the armature iron core to the inside of the magnetic-field-pole iron core, characterized in that the magnetic-field-pole iron core is formed from two or more kinds of thin laminated plates (A, B) having different shapes, wherein the magnetic resistance element is provided in at least one kind of the thin plates (A, B), wherein the two or more kinds of thin plates (A, B) are stacked on top of each other so as to vary the shape of the slit (13, 14, 19, 22, 23), thereby adjusting the magnetic resistance, and wherein letting h1 and h2 denote the width of the slit (13, 14, 19, 22, 23) in the circumferential direction of the magnetic-field-pole iron core and the depth of the slit (13, 14, 19, 22, 23) in the radial-direction thereof, respectively, the slit (13, 14, 19, 22, 23) is configured in such a way that h2/h1 is larger than 1.0, wherein a minimum slit pitch θ given in electric angle is θ = 180°, or θ = 60°, or θ = 35°, or θ = 30°, or θ = 25°, or θ = 20°.