PURPOSE: To make clamps shorter and enhance economy and operability, by providing annular grooves at both outside end parts of bearings for a carrier, providing a slant surface at least one of an outer peripheral surface of a tip part of a clamp and an inner peripheral surface of the groove, and fitting the tip parts into the grooves.

CONSTITUTION: Annular grooves 33a, 33b are provided at the outside end parts of bearings 32a, 32b supported by the cylindrical body 31 of a carrier 26. Clamps 35a, 35b are fitted to a support shaft 24 on both sides of the carrier 26 by pressing cuts 36a, 36b of the clamps against a shaft 24, and the tip parts of the clamps 35a, 35b are fitted respectively into grooves 33a, 33b, upon which the outer peripheral surfaces of the tip parts of the clamps 35a, 35b are brought into contact with inner peripheral surfaces (slant surfaces) 34a, 34b of the grooves. Accordingly, the carrier 26 can be efficiently prevented from being moved during transportation, and the clamps 35a, 35b can be made shorter.