A deviation between a target value of a quantity of state and an actual value of the quantity of state that is caused to follow the target value or a time-integral of the deviation is filtered. Based on the filtered value, a switching surface &sgr; is calculated. Based on a value of the switching surface &sgr;, a control input value u is outputted. The filter is set through comparison in Bode diagrams between a design model of a control system based on an ordinary sliding mode control method and a characteristic variation model of the control system, and by performing compensation in such a direction as to cancel out the variation. The filtering process makes it possible to properly control the control system having a dead time by the sliding mode control method.