PURPOSE: To obtain proper braking force distribution regardless of whether the braking is quick or slow by providing a correcting means to correct air pressure fixed in the input section of a brake controlling means according to the pressure of a front side air suspension.

CONSTITUTION: In the case of applying a quick brake, since a load does not quickly transfer forward to a large extent, axle-weight characteristics becomes larger in a rear side and smaller in a front side. In this case, because the load does not transfer, an increase in the air pressure of air springs 33 and 34 is small. Therefore, the turning movement of an arm member 43 is small, and the pressure correction quantity of the input section 17a of a load sensing valve 17 is small. For this reason, even if a quick brake is applied, proper braking force distribution can be obtained.