PURPOSE: To suppress the rotation of a trunnion shaft and secure the driving force of a rear-rear axle when a rear biaxial vehicle tends to take a forward tilting attitude by providing a trunnion brake applying a brake to the rotation of the trunnion shaft assembled with leaf springs.

CONSTITUTION: A large truck 40 driven with a rear-front axle 44 and a rear-rear axle 45 is provided with a trunnion shaft 11 supported on the side rail 42 of a rear suspension 10 by a bracket 12 and leaf springs 13 supported at the right and left ends of the shaft 11. A trunnion brake 20 applying a brake to the rotation of the trunnion shaft 11 is provided at one of the right and left trunnion housings 21 assembling the right and left leaf springs 13 to the trunnion shaft 11. When this vehicle is traveled on a rough road such as a muddy road, the brake 20 is operated to apply a brake to the rotation of the shaft 11, the forward tilting attitude of the rear suspension 10 is suppressed, and the sufficient driving force of the rear-rear axle 45 is secured.