Each of plural slots has a slot peripheral wall SW and a slot opening 53d. The slot peripheral wall SW has a slot bottom wall 53a, a pair of slot side walls 53b and 53c opposing to each other and continuing to end portions of the slot bottom wall 53a, and is covered with an insulation coating 55 made of an electrical insulation material. The insulation coating 55 is formed over continuously from the slot bottom wall 53a to the pair of slot side walls 53b and 53c, and a pair of holding grooves 56 opposing to each other is formed in the insulation coating 55 at the vicinity of the slot opening 53d. The groove walls CW of the pair of the holding grooves 56 are formed in the insulation coating 55, and an electrical insulation member 57 to close the slot opening 53d is inserted in the pair of holding grooves and held between the pair of holding grooves 56.