To reduce costs.

A base bracket 1 has a mounting hole 12, into which a cylindrical collar 13 is fitted to be retained, and is fixed to a vehicle body by a bolt B inserted through the collar 13 fitted into the mounting hole 12. The mounting hole 12 has a counterbored part 12a, where the diameter of the hole is widened, at least on one opening end, and the collar 13 has a connecting stopper click 14 on one end and the other end in the axial direction so as to be fixed to the mounting hole 12. The connecting stopper click 14 is formed so as to gradually project outward in the radial direction from a supporting point 14a on the rim side of the collar 13 in the axial direction to the connecting stopper end 14b on the central side of the collar 13 in the axial direction.