A processor acquires a steering torque detected by a steering torque sensor and a vehicle speed detected by a vehicle speed sensor, changes a gain and a phase to be applied to the steering torque in accordance with a steering frequency when a driver steers a steering wheel, determines a magnitude of an assist torque based on the steering torque to which the gain and the phase have been applied and the vehicle speed, and generates a torque command value to be used to control driving of the motor based on the determined assist torque.