A plurality of single-pole coils are retained by a coil retaining device, the single-pole coils are arranged such that the coil insertion portions of each single-pole coil confront the inner circumference openings of the slots and may be generally parallel to the axial direction of the motor core, each single-pole coil is moved linearly toward the motor core such that the coil retaining device and the moving locus before the adjoining coil insertion portions in the adjoining single-pole coils are inserted into the slots are parallel or approach the more from the inner circumference side to the outer circumference side and the two coil insertion portions of each single-pole coil are moved such that they may start their movements simultaneously and at equal velocities.