An armature winding includes a plurality of strand groups each having strands transposed and bound in at least two rows and multiple tiers, and a main insulator for covering the strand group. A flow resistance of a current passing though the strands on an upper and a lower side in the cross-section of the strand group is set larger than a flow resistance of a current which passes through the strands in a central portion, or a flow resistance of a current passing through at least one of the plurality of strand groups is set larger than a flow resistance of a current passing through the remaining strand groups.