PURPOSE: To secure a departure on a bad road, prevent a slip of a driving wheel, and previously avoid racing by applying a load utilizing pressure to be changed into predetermined plural pressure values in the raising direction to rear two axles, and coping with a loading condition and a traveling condition of a rear two-axle car.

CONSTITUTION: An air bag 11 which is supported with frames 41 and 41 and can apply a load in the raising direction to a driving wheel axle 42 is provided. A load is generated in the air bag means 11 by utilizing pressure to be changed into either of plural pressure values 6.0kgf/cm2 and 3.7kgf/cm2 predetermined according to a loading condition and a traveling condition of a truck 40, and its generating load is applied in its raising direction to its idler wheel axle 43. Of course, when its truck 40 departs under comparatively heavy loading or heavy loading, or when it travels on an ordinary road in its loading condition, its axial load distributing method and a device 10 put its air bag means 11 in a condition of exhaust pressure of 0.5kgf/cm2, and do not perform a function to move an axial load.