PURPOSE: To uniform axle load applied to two rear shafts which are a driving shaft and a driven shaft without harming the characteristic of a trunnion suspension.

CONSTITUTION: An auxiliary spring 20 for receiving load from a frame 1 is provided on the driven shaft 8 side between two rear shafts which are a driving shaft 7 and a driven shaft 8. Spring bearings 23 are provided to come in contact with the auxiliary spring 20 when the loadage to the frame 1 becomes the specified value or more. Accordingly, when the loadage becomes the specified value or more, the difference between the axle load applied to the driving shaft 7 and the axle load applied to the driven shaft 8 is reduced to uniform the axle load of the driving shaft 7 and that of the driven shaft 8.