PURPOSE: To provide an axial load adjustment device for a trunnion type suspension, capable of automatically adjusting an axial load according to a load acting on a rear shaft, and increasing a slip limit in an empty car condition without extremely increasing a load acting on a driving shaft.

CONSTITUTION: Space between a rear shaft 5 and a body frame 1 is provided with an air spring 13 for reducing a load on the rear shaft 5 as a driven axle upon the supply of the air and increasing a load ratio on a front shaft 4 as a driving axle, and a leveling valve 11 for detecting a vertical load on the rear shaft 4 and supplying the air pressure from an air tank to the air spring 13 under an empty car condition.