Abstract: A stator coil has tooth portions and slot portions defied between adjacent tooth portions. Each tooth portion has a rectangular cross-section perpendicular to the axis of the stator core. A group of conductor wires received in each slot portion includes conductor wires of a circular cross-sections and conductor wires having polymorphic cross-sections. The ratio (space factor) of the overall cross-sectional area of the conductor wires accommodated by the slot portion relative to the cross-sectional area of the slot portion is not less than 80%.