PURPOSE: To apply assist force, which is set for a change in actual steering torque, to a steering system, in a motor-driven pump type power steering device, by correcting a deviated amount of a detected torque by a torque detection means from a value corresponding to actual steering torque, if any.

CONSTITUTION: The detected torque V when the load current I of a motor which drives a hydraulic pump is a prescribed amount IS is set as updated right or left steering torque VR, VL, by the magnitude to the neutral value VN at the present point (steps S104-S108) to compute and update the neutral value VN from the updated right steering torque VR and the updated left steering torque VL (steps S109-S110) and correct the detected torque V based on the updated neutral value VN.