PURPOSE: To prevent abrasion or damage on a traction hook by providing an oil supply tank at the rear of a tractor and by arranging a pipe from the oil supply tank on a draw-bar pin and an eye bolt for oil supply so as to supply oil to the traction hook of the tractor.

CONSTITUTION: An oil supply tank 2 is provided at the rear of a tractor, and base ends of pipes 8 and 9 are connected to flow-rate regulating cocks 6 and 7 provided at an outlet 5 below the tank. And a tip end of a pipe 8 is arranged on a draw-bar pin 13 connecting a draw-bar hook 11 at the rear of the tractor to a crevice 14 on a body for traction. And a tip end of the pipe 9 is arranged on an eye bolt 17, and the tip end of the pipe 9 is connected to a T-shaped nozzle 18 on the eye bolt 17 so as to flow oil from both sides of the eye bolt 17 down to a crevice pin 15. By this, a friction face between the draw-bar hook and the crevice and the friction face between the eye bolt and the crevice is made smooth and friction is reduced, whereby abrasion or damage on parts can be prevented.