To effectively use a canopy roof by constituting a roof support so as to rise and fall freely, and supporting a canopy roof so that it can be fixed at a position where it functions as a screed as a screed step roof.

In using a canopy roof 6 of a main driver's seat 3 as a screed step 20 roof, when a rod 70 of a hydraulic cylinder 7 is shrunk, a movable part 51 of a roof support 5 and an auxiliary support 9 fall in cooperation by means of a link mechanism where axial connection lines of pins 53, 54, 55, 56 form a parallelogram. The roof 6 moves parallely to a position above a position of a step 20 control handle 21, which is raised owing to vibration, to thereby covers all equipment disposed in the step 20 and the screed part 2. At the time of returning the roof to the original position, the rod 70 is elongated to erect the movable part 51 and the auxiliary support 9. Accordingly the canopy roof 6 can also be used as the screed step 20 roof.