A measuring arm (12) is attached to a frame (5a) supporting a screed (5). Height sensors (13) and (14) are attached to the measuring arm (12), and a height sensor (19) is also attached to the arm (18) of the screed (5). The spacing must remain constant between the rear end of the screed (5) and the height sensor (19), between the height sensor (19) and the height sensor (14), and between the height sensor (14) and the height sensor (13). A distance sensor to calculate the travel distance is provided on the tractor unit (1). The relative height Ho of both height sensors (13) and (14) to the screed (5) must always remain constant, regardless of the tilt of the screed (5) and the measuring arm (12). The sensors (13), and (14), and (17) are connected to the arithmetic unit (30). The height sensor (19) is connected to the arithmetic unit (40). The arithmetic unit (30) receives an output signal from the height sensors (13) and (14) and calculates the thickness of the pavement. The arithmetic unit (40) detects the uneven level of the unpaved surface on the basis of the output signal from the height sensor (19) and controls the screed (5) in order to offset the unevenness.The operating conditions are set on the control unit (30) via a recording medium such as an IC card.