PURPOSE: To improve stiffness and safety in a connected state white maintaining the ease of connection and removal work.

CONSTITUTION: A connecting hitch 9 is installed to a tractor main body 1 while a connecting frame 10 is installed to the rear end of a lift arm 3, thereby engaging a first hook of the connecting hitch 9 with a first pin 10a of the connecting frame 10. A cylindrical body of the connecting hitch 9 is engaged with a second hook in relation to this engagement so that a second pin hole may be aligned with a second pin hole of the connecting frame 10. Then, a second pin 14 is removably inserted into both second pin holes.