To make either of operations in angle motion or tilt motion executable with a single hydraulic cylinder by changing a installation position of the hydraulic cylinder supporting a blade.

On executing operations in tilt motion, a connecting rod 36 is arranged at the upper part and a hydraulic cylinder 43 is arranged thereunder at one side of a C-shaped frame 11 supporting a blade 15. As the hydraulic cylinder 43 is expanded, a connecting rod 53 is moved through a bell crank 52, pushing the upper part at the opposite side of the blade 15, and thereby the blade 15 makes tilt motion round a longitudinal shaft member 22 of the main connecting member 21 at the lower part of the blade. In the case of executing operations in angle motion, the positions of the connecting rod 36 and the hydraulic cylinder 43 are exchanged, and the tip of the piston rod of the hydraulic cylinder 43 is connected directly to a bracket 35 of the blade 15. Therefore, as the hydraulic cylinder 43 is expanded, the blade 15 makes angle motion round the vertical shaft members 24, 57 at the opposite side.