PURPOSE: To simplify the structure and improve the durability by slidably engaging a rod of a hydraulic actuator with a member which is fit to the supporting element of a cab via a rotor and by providing a contact member for the rod so as to elevate the rotor.

CONSTITUTION: A rotor 3a is muouted via bearing members 3m and 3n to a supporting element 3 which is secured to a cab 1. A member 3b having a convex spherical bearing face 3i si sliidably pivoted to a concave spherical bearing face 3c of a bearing member 3r which is fit inside a drilled hole 3a of the rotor 3a. A rod 5 of hydraulic actuator 4 for raising the cab 1 is fit in the drilled hole 3d of the member 3b in the axially silidable relation. A rail 3e having a concave spherical face is stuck to the supporting element 3. A contact member 5a which comes into contact with the side face end 3g of the rotor 3a when the cab 1 is inclined is threadably engaged with the rod 5, the back face 5b of the contact member 5a having th convex spherical face. When the cab 1 is tilted, the back face 5b of the convex spherical face may slide on said rail 3e.