PURPOSE: To let a cab absorb its up-and-down motion and thereby make the vertical moving force controllable from its acting on a hydraulic cylinder, by installing a lost motion mechanism, comprising a link mechanism, in position between a link lever and the cab.

CONSTITUTION: In time of car running, a cab 3 supported on a suspension 2 moves up and down on a body frame 1. In time of this vertical motion, a lost motion link 8 receives any motion in a second link 8b being coupled with the side of the car 3 and is forced to move up and down through expansible motion in a first link 8a, absorbing the cab's vertical motion while being expanded or bent. With suchlike lost motion, the cab's vertical motion being transmitted to a link lever 6 is controllable, thus any force making such an up-and-down motion is preventable from its acting on a hydraulic cylinder 7.