A greasing through hole is perforated through one outer link plate, and greasing device is attached to the through hole. Degreasing through-holes are perforated through an outer link plate or an inner link plate on the side distant from the outer link plate with a bearing section A between the link plates, and degreasing device 22 is attached to those through-holes. Lubricant injected from the greasing device is supplied to the bearing section A through a gap c between the sealing device and the outer link plate, and used lubricant within the bearing section A is discharged out of the degreasing device through another gap c.