This study aimed at simultaneously achieving realization of ride comfort and steering stability through controller design for semi-active suspension taking into consideration the most sensitive frequency range of the human body and vehicle behavior when steering. A method that can improve both ride comfort and vehicle stability is proposed by separating the control range in terms of the frequency domain, where the frequency weighting in controlled variables is used. Furthermore, the controller is scheduled in the time domain to attain a positive pitch angle during slaloms. The dynamics of road disturbance is assumed and is accommodated into the controller to make control more effective. Computer simulations were carried out to investigate the effectiveness of the proposed control system by using a full-vehicle model that had a variable stiffness and damping semi-active suspension system. As a result, it was demonstrated that the proposed method can improve ride comfort, reduce vehicle motion, and synchronize the roll and pitch motions caused by steering.