A plurality of coils concentratedly wound around individual teeth are formed as coil units having a common shape, each of the coil units being made by winding a conductor in a generally rectangular form, stacking one conductor line on top of another, and each of the coil units having two parallel straight portions inserted into the slots on both sides of each tooth. The two parallel straight portions of the conductor of each coil unit are fitted in two adjacent slots in such a way that one straight portion of the conductor is laid in an inner layer in one of the two adjacent slots and the other straight portion of the conductor is laid in an outer layer in the other of the two adjacent slots.