A calculator or an electronic control unit (ECU) calculates an instruction value of a column assist torque and a rack assist torque output from a column actuator, or a column motor, and a rack actuator, or a rack motor, based at least on a torsion torque. The calculator includes a base assist controller, a stabilization controller, and an adder. The base assist controller individually or commonly calculates a base assist torque based on the torsion torque. The stabilization controller individually or commonly calculates a stabilization torque for stabilizing a steering system. The adder performs addition of the base assist torque and the stabilization torque.