Abstract: A coupling pin 20 is inserted through insertion holes of both end plates such that a head portion 20a thereof abuts an end plate 104 of one segment 1a and inclined surfaces S3 of notch portions 20c and 20d protrude from an end plate 105 of the other segment 1b. A clamp member 30 is disposed at a position where the inclined surface T2? of a leg portion 30b faces the inclined surface S3 of the notch portion, and the leg portion of the clamp member is press-fitted into the notch portion such that the inclined surface thereof is brought into surface contact with the inclined surface of the notch portion. The end plates of both the segments are clamped and both the segments are coupled in the circumferential direction due to movement of the clamp member toward the segment end plate direction corresponding to the angle of inclination of the leg portion, the movement being generated by the press-fitting of the leg portion of the clamp member.