PURPOSE: To allow accurate dimensional setting of an opening at a reversed inserting part by coupling a guide body at the ends thereof on the opposite sides of the reversed inserting part and enhancing the strength thereby retarding the deformation when pressure is applied or temperature varies.

CONSTITUTION: A guide body 21 has a coupling 80 between a protruding surface part 74 and a recessed surface 75 facing each other through a reversed inserting part 73. This structure enhances the strength and even when the guide body 21 is subjected to external pressure in the radial, circumferential or torsional directions or when the indoor temperature varies within a range of -40°-+100°C, the guide body 21 can be rotated smoothly along the groove part of the stator while sustaining the shape thereof and the dimensions of opening at the reversed inserting section 73 can be set accurately.