To link one working machine to plural kinds of connecting frames.

A connecting frame 6 is linked through a top link 3 and a three-point link mechanism 5 having a pair of right and left links 4 to a tractor body 2. An upper connecting part 7 and a pair of right and left lower connecting parts 8 are formed on the connecting frame 6 and engaged with an upper engaging part 10 and a pair of right and left lower engaging parts 11 of a working machine 9, respectively. A PTO shaft 12 of a tractor body 2 is linked to a PIC shaft 13 of the working machine 9 by a joint shaft 14. At least either of the upper engaging part 10 or the lower engaging parts 10 is installed changeably in position in the vertical direction and/or the longitudinal direction based on the PIC shaft 13 of the working machine 9.