A suspension system of a vehicle which judges the direction of a damping force of a shock absorber of damping force characteristic variable type, provided between the sprung member and the unsprung member, either oscillation-stimulating direction or oscillation-restraining direction with respect to vertical osciallation of the sprung member, and it also judges the size of the damping force of the shock absorber. The damping force characteristic of the shock absorber is set higher when it is larger than the predetermined value and it is set lower when it is less than the predertemined value. The predetermined value can be changed according to the road surface, oscillation-restraining energy becomes larger than the oscillation-stimulating energy thereby. Therefore, improvement of the comfortableness to ride in and running stability can be planned and also, noise and oscillation caused by unnecessary changes of the damping force characteristic of the shock absorber in a high oscillation frequency range due to road bumps can be reduced.