Abstract: A servo controller calculates a base assist command so that a steering torque follows a target steering torque. An estimated load torque calculation section calculates an estimated load torque based on a target steering torque and a base assist command. A target steering torque calculation section calculates a target steering torque using a map that defines a relationship between the estimated load torque and the target steering torque. The servo controller has a low-pass filter for removing high-frequency components of a predetermined frequency or higher in the input target steering torque at least in a differential control calculation, and calculates a differential control amount according to a steering torque deviation between the target steering torque after the low-pass filter and the steering torque.