1. A suspension control system comprising: a shock absorber of a variable damping characteristic type interposed between sprung and unsprung members of a vehicle; an actuator for changing damping characteristics of said shock absorber; a velocity detecting device for detecting the velocity of movement of said sprung member; a piston speed estimating device for estimating a level of piston speed of a piston performing sliding movement inside said shock absorber; and a controller having a plurality of damping force maps showing relationship between damping force and an actuator command signal, respectively in correspondence to various levels of said piston speed; wherein said controller obtains necessary damping force from the velocity of said sprung member, and further, said controller selects a damping force map corresponding to the level of piston speed estimated by said piston speed estimating device and outputs said actuator command signal on the basis of the selected damping force map.