PURPOSE: To give good steering performance to a rear axle and prevent the rear wheels from side-slipping when cornering by steering around an axis in the lateral direction of a vehicle a rear axle which is provided with knuckles for supporting the rear wheels at both ends in the lateral direction of the vehicle via kingpins and providing an actuator for changing a caster angle of the rear wheels.

CONSTITUTION: A vehicle having two rear axles of trunion type includes a rear front axle 28 and a rear back axle 30 which are supported respectively on a front part and a rear part of a suspension spring 22 at both ends in the lateral direction of the vehicle. In this respect, the rear back axle 30 is provided with knuckles 62 which support it with an upper and a lower saddles 32 such that it can rotate around an axis and is rotatably supported via kingpins 60 on both ends in the lateral direction of the vehicle body. A bracket 50 on a cross member 14 is connected to a projecting bracket 52 on an intermediate section of the rear back axle 30 by an upper radius rod 54 with an actuator therebetween such that the rear back axle 30 can be steered around the kingpin 60 by the actuator 56.