A front side of a floor panel (15) is pivotally supported on a floor panel support mechanism (21), permitting tilting of the floor panel in a forward direction with respect to a revolving frame (5) by way of a tilting mechanism (30). The tilting mechanism (30) has a guide rail assembly (33) which is pivotally supported on the side of the revolving frame (5), a screw rod (34) which is rotatably supported on the guide rail assembly (33), and a displacement member (35) which is attached to the floor panel (15) and held in threaded engagement with the screw rod (34). The floor panel (15) and a cab (29) are tilted up in the forward direction upon rotationally driving the screw rod (34) to translate the displacement member (35) constituting the tilting mechanism (30).