Abstract: The quantity that a brake pedal 5 disposed inside a cab is stepped on is communicated to a link 10a through rods 9a and 9b, and rotates a shaft 23. The rotation of the shaft is communicated through a link 10b to a rod 9c, and a push rod 27 of a hydraulic booster 2 is pushed in by a link 10c. An adjuster 15 connecting the rod 9a and the rod 9b supports the rod 9a enabling a slide movement in the axial direction, and at the same time forces both rods in the direction to extend away from each other by a spring disposed inside. The relative displacement of the chassis frame and the cab is absorbed by the adjuster.