PURPOSE: To provide such a simply-structured rear axle suspension for a rear two-axle vehicle as having high running ability on bad roads.

CONSTITUTION: The middle of a leaf spring 4 is mounted to a frame 1 via a trunnion shaft 2 and a trunnion bracket 3. After it is constructed by a drive shaft, front axle 6 is mounted at the front end of the leaf spring 4. On the other hand, after it is constructed by a fixed shaft, a rear axle 7 is mounted at the rear end of the leaf spring 4. By providing an auxiliary spring 12 between the rear axle 7 and the frame 1 to lift and energize the rear axle 7, the weight of the front axle 6 in a light load area is increased and corrected equivalent for the lifting and energizing force of the auxiliary spring 12 to reduce the rate of slipping.