To heighten lowest ground clearance and reduce a manufacturing cost by fixing the upper part of a trunnion with both ends fixed to an intermediate rear axle and a rear axle to a longitudnal frame, and fixing the upper part of a lateral rigid part with both ends fixed to the intermediate rear axle and the rear axle, to a lateral frame.

The upper parts of two trunnion parts 20 are fixed to a longitudinal frame 2, and both ends are respectively fixed to an intermediate rear axle 8 and a rear axle 6. The upper parts of two lateral rigid parts 40 are fixed to a lateral frame, and both ends are respectively fixed to both sides of the intermediate rear axle 8 and both sides of the rear axle 6. Each trunnion part 20 is fixed to the longitudinal frame 2 by a trunnion base 22. A lower saddle 24 is connected to the trunnion base 22, and a laminated leaf spring 26 is further fixed by a bolt 27. Both ends of the leaf spring 26 are respectively installed at the intermediate rear axle 8 and the rear axle 6 at leaf spring fixing parts 28. As a result, a radius-rod is not used so as to reduce the load of the trunnion parts 20.