A permanent-magnet motor comprising: a stator core in which a plurality of electromagnetic steel sheets are stacked in an axle direction and in which teeth and slots are alternately formed in a circumferential direction; an armature coil that includes a conductor inserted into the slot and is mounted in the stator core; a rotor core in which a plurality of electromagnetic steel sheets are stacked in the axle direction and that is disposed in such a way that the outer circumferential surface thereof faces the inner circumferential surface of the stator core via a predetermined gap; and a plurality of permanent magnets (41, 41a, 41b) that are embedded in the rotor core and form a plurality of magnetic-field poles in the rotor core, wherein the rotor core includes a plurality of through-holes (23b, 23c, 23b1, 23b2) arranged in such a way as to be spaced via a distance apart from one another around the center axis of the rotor core, a plurality of through-hole expansion portions, each of which is provided in couple with corresponding each of the plurality of through-holes (23b, 23c, 23b1, 23b2), and a bridge portion that is situated at the boundary portion between the magnetic-field poles, surrounds the adjacent through-hole expansion portions, and forms part of the outer circumferential surface of the rotor core, wherein each of the plurality of permanent magnets (41, 41a, 41b) is embedded in the rotor core in such a way as to be inserted into corresponding each of the plurality of through-holes (23b, 23c, 23b1, 23b2), and wherein the radius of the rotor core at the bridge portion is smaller than the radius of the rotor core at a portion other than the bridge portion, characterized in that the armature coil is configured with at least two groups of coils that are formed in substantially the same manner, wherein when Wb denotes the radial-direction minimum width, at the bridge portion, of the rotor core, tb denotes the thickness, at the bridge portion, of the electromagnetic steel sheet, tr denotes the thickness, at the portion other than the bridge portion, of the electromagnetic steel sheet, and Wa denotes the minimum distance with which the adjacent through-hole expansion portions face each other, the bridge portion is formed in such a way that at least one of the equations,, and below is satisfied Wb ≦ tb = tr tb ≦ tr Wa ≦ tb a stator core in which a plurality of electromagnetic steel sheets are stacked in an axle direction and in which teeth and slots are alternately formed in a circumferential direction; an armature coil that includes a conductor inserted into the slot and is mounted in the stator core; a rotor core in which a plurality of electromagnetic steel sheets are stacked in the axle direction and that is disposed in such a way that the outer circumferential surface thereof faces the inner circumferential surface of the stator core via a predetermined gap; and a plurality of permanent magnets (41, 41a, 41b) that are embedded in the rotor core and form a plurality of magnetic-field poles in the rotor core, wherein the rotor core includes a plurality of through-holes (23b, 23c, 23b1, 23b2) arranged in such a way as to be spaced via a distance apart from one another around the center axis of the rotor core, a plurality of through-hole expansion portions, each of which is provided in couple with corresponding each of the plurality of through-holes (23b, 23c, 23b1, 23b2), and a bridge portion that is situated at the boundary portion between the magnetic-field poles, surrounds the adjacent through-hole expansion portions, and forms part of the outer circumferential surface of the rotor core, a plurality of through-holes (23b, 23c, 23b1, 23b2) arranged in such a way as to be spaced via a distance apart from one another around the center axis of the rotor core, a plurality of through-hole expansion portions, each of which is provided in couple with corresponding each of the plurality of through-holes (23b, 23c, 23b1, 23b2), and a bridge portion that is situated at the boundary portion between the magnetic-field poles, surrounds the adjacent through-hole expansion portions, and forms part of the outer circumferential surface of the rotor core, wherein each of the plurality of permanent magnets (41, 41a, 41b) is embedded in the rotor core in such a way as to be inserted into corresponding each of the plurality of through-holes (23b, 23c, 23b1, 23b2), and wherein the radius of the rotor core at the bridge portion is smaller than the radius of the rotor core at a portion other than the bridge portion, characterized in that the armature coil is configured with at least two groups of coils that are formed in substantially the same manner, wherein when Wb denotes the radial-direction minimum width, at the bridge portion, of the rotor core, tb denotes the thickness, at the bridge portion, of the electromagnetic steel sheet, tr denotes the thickness, at the portion other than the bridge portion, of the electromagnetic steel sheet, and Wa denotes the minimum distance with which the adjacent through-hole expansion portions face each other, the bridge portion is formed in such a way that at least one of the equations,, and below is satisfied Wb ≦ tb = tr tb ≦ tr Wa ≦ tb