A steer-by-wire system includes a turning device that turns a vehicle wheel; and a steering reaction force control unit that controls a steering reaction force applied to a steering wheel. The steering reaction force control unit is configured to calculate a plurality of kinds of axial forces, calculate a final axial force based on the axial forces, and generate the steering reaction force corresponding to the final axial force. The axial forces include a basic axial force, and an under axial force that becomes smaller than the basic axial force during understeer. The steering reaction force control unit is configured to calculate a degree of understeer reflecting a difference between the basic axial force and the under axial force during the understeer and to reduce the final axial force during the understeer to a value smaller than the basic axial force by an amount corresponding to the degree of understeer.