In a stator having a stator core and three phase windings, slots are formed in the stator core. The phase winding are accommodated in layers, from one side to the other side in the corresponding slot along a radial direction of the stator core. The phase windings are arranged in a star-delta composite connection structure. The phase winding in each phase is comprised of conductors accommodated in a first slot and a second slot adjacently arranged in the stator core so that the conductor in the n-th layer is electrically connected to the conductor in the (n+1)-th layer, ascending order, per slot. Because each winding has the same length and no difference in electric potential occurs between the star connection and the delta connection, this structure suppress generation of operation noise and a circulating current through the stator core and prevents loss due to the circulating current.