PURPOSE: To layer and level up soil and sand to uniform thickness by providing a driver to regulate the height of a leveler, a level detector to rub the surface of ground, and a controller to operate the driver in such a way as to make the level coincide with a set value.

CONSTITUTION: When leveling soil 5 to a desired thickness (h), a thickness setter 18 is adjusted to make setting in such a way as to make the height from the ground 6 to the downside of a blade 9 the value (h). When a motor grader is run, since a level detection bar 11 is pulled downwards by a return spring 12, the tip of the bar 11 is always buried in the layer of soil 5 and moved while rubbing the ground 6. In case that the height between the tip of the bar 11 and the downside of the blade 9 is deviated from the set value (h), the deviation between the detected value of the sensor 10 and the set value (h) is transmitted from a mixer 19 to an arithmetical circuit 16. A correction output signal is then sent to an oil-pressure driver 15, and a lift cylinder 3 is operated so that the difference in height between the tip of the bar 11 and the downside of the blade 9 is restored to the set value (h).