DEVICE FOR ESTIMATING DRIFT AMOUNT OF LATERAL ACCELERATION SENSOR, DEVICE FOR CORRECTING OUTPUT OF LATERAL ACCELERATION SENSOR, AND DEVICE FOR ESTIMATING ROAD SURFACE FRICTION STATE

An SAT estimating section estimates self-aligning torque (SAT) on the basis of a steering torque, which is detected by a steering torque detecting section, and an assist torque, which is detected by an assist torque detecting section. An SAT model value computing section computes an SAT model value by using an integrated slip angle αI. An SAT ratio/drift amount computing section computes, by on-line identification, a ratio (SAT ratio) of the SAT to the SAT model value, and a drift amount of a lateral acceleration sensor.