To prevent seizure of a sliding bearing and a roller.

The sliding bearing 6 and the rollers 5 are rotatably provided on a supporting shaft 4 arranged on a pair of side walls 2, 3 facing each other, respectively. The width L6 of the sliding bearing 6 in the axial direction is determined to be narrower than the width L5 of the roller 5 in the axial direction in order to form a space 9 for storing lubricant inside the roller 5. The lubricant stored in the space 9 is supplied from the space 9 to the region between the roller 5 and the sliding bearing 6. An oil passage 8 (13) for supplying the lubricant from the side wall 3 side to the outer periphery side of the supporting shaft 4 may be formed in the supporting shaft 4. Further, a through-hole 10 passing through in the radial direction may be formed in the sliding bearing 6.