An insulator includes a part to be wound with a coil of a wiring wire with a circular cross section; first and second flanges. The first flange is formed at the side of the part closer to a core segment. The second flange is formed at the side closer to a distal end of a tooth. The part to be wound with the coil has a slope continuous with the first flange and inclined so that a height from an upper surface of the tooth increases from the first flange toward the second flange. Expression 0