PURPOSE: To prevent coming-off of a pin which connects track links each other surely by a bolt and a nut and improve workability in tightening it.

CONSTITUTION: A mating boss portion 10B is inserted between bracket sections provided on a track link 8 of a crawler belt to connect them by a pin 15. An engaging stepped section 32 which engages with a flat portion 17A of a nut 17 and locks the nut 17 is provided in a mounting section 31 of a bracket section 10A. Consequently, when the crawler belt is driven and runs, the pin 15 is pushed in the arrow A direction, and even if it collides against the nut 17 repeatedly, rotary force does not generate in the nut 17, and the loosening of the nut 17 is prevented securely.