In an armature coil according to the present invention and, more particularly, in an armature coil including a plurality of coil conductors wound around a plurality of slots which are formed in a stator core and opened on the radially inner side, the circumferential width of the plurality of the coil conductors is formed in a substantially trapezoidal shape which gets narrower toward the radially inner side and the cross-sectional areas of the plurality of the coil conductors in the slot are each substantially the same and the circumferential width thereof is formed narrower as the coil conductor is arranged toward the radially inner side; and one coil conductor is formed in a convex shape and another coil conductor is formed in a concave shape along the convex shape.