PURPOSE: To effectively prevent racing of a driving wheel by providing a driving force addition control means for automatically increasing the share of a load placed on a driving axle when a movable load is lower than a set value and a car speed is from a very small value including zero to a specified value.

CONSTITUTION: A driving axle weighting device is provided with a load sensor 2 for detecting the mechanical displacement of a leaf spring 1 placed between an axle and a car frame and outputting a movable load signal, a car speed sensor 3 and a brake switch 4. The device also provided with an air spring 7 in parallel with the driving axle for sharing of a load placed on a driven axle 6 for sharing a load and by controlling a solenoid valve 8 for controlling supplying and discharging of compressed air to and from this air spring by a control circuit 9, sharing of the load is changed. This control circuit 9 controls the solenoid valve 8 so as to increase the load share applied to a driving axle 5 when a movable load is lower than a set value and a car speed is from a very small value including zero to a specified value.