To fix a bearing plate to a yoke and an end plate with a simple structure.

In a state where a protrusion 63 is moved to an engaging hole 71b, a bearing plate 6 is in such a state that the extension surface 63a of the protrusion 63 abuts against an end plate 7 from the upper side, and the outer end face 64 abuts against the end plate 7 from the lower side. More specifically, the bearing plate 6 is coupled so as to sandwich the end plate 7 from above and below. Since the radius of outer periphery of the bearing plate 6 is equal to the radius of the inner peripheral surface 45 of an outer yoke 42, the bearing plate 6 does not move in the horizontal direction in the outer yoke and the position is maintained at an end, by simply fixing the end plate 7 to the end of the outer yoke 42. The bearing plate 6 is not interposed between the end plate 7 and the outer yoke 42, but the outer peripheral surface thereof simply abuts against the outer yoke 42.