PURPOSE: To shorten the spring length by integrally and vertically moving four links with two rocking arms and an auxiliary link, and displacing a spring member fixed with both ends to two opposite junctions of four junctions when a wheel bounds or rebounds.

CONSTITUTION: The first and second rocking arms 18, 20 and a connecting arm 22 are pivotally supported on a front bracket 12, and the connecting arm 22 and an auxiliary link 26 are pivotally supported on a rear bracket 14. The first and second links 30, 32 are connected to the auxiliary link 26, the first rocking arm 18 and the third link 36 are connected to the first link 30, and the second rocking arm 20 and the fourth link 40 are connected to the second link 30 respectively. A rear axle 42 is fixed to the junction of the third and fourth links 36, 40, and a coil spring 36 is provided between the first and second junctions located in the vertical direction. Four links 30, 32, 36, 40 are integrally and vertically moved, the coil spring 46 is displaced within the links 30-40, thus the spring length is shortened.