PURPOSE: To achieve accurate and quick coupling of a working machine to a tractor by contracting a top link in the scooping and attaching of a triangular frame.

CONSTITUTION: A coupling member 14 is scooped from the lower coupling parts 18, 18 by the extension of a top link 10 in the course of approaching a tractor 1 toward a working machine and is swingably held with coupling parts 22, 22 at the rear side close to the working machine R. The scooping and coupling part 22 is positioned below an upper engaging part 88, a three-point link mechanism 9 is raised to couple the scooping and coupling part 22 to the upper engaging part 88 and is further raised while contracting the top link 10 to transfer the lower coupling parts 18, 18 of the coupling member 14 around the upper engaging part 88 toward the lower engaging part 89 of the working machine R until the working machine R is coupled to the tractor.