To measure the loaded weight of a dump truck, accurately and
inexpensively. In a dump truck comprising a set of equalizer bars
respectively provided rotatably on the left and right-hand sides of a
vehicle body; first vehicle wheels supported respectively by means of
first suspension devices on one side of each equalizer bar; second
vehicle wheels supported respectively by means of second suspension
devices on the other side of each equalizer bar; and third vehicle wheels
provided respectively on the left and right-hand sides of the vehicle
body separately from the equalizer bars, and being supported respectively
by means of third suspension devices; a first load applied to the second
suspension device is detected; a second load applied to the third
suspension device is detected; the angle of inclination of the vehicle
body is detected; and a loaded weight is calculated on the basis of the
first and second loads, and the angle of inclination.