to provide a controller for an electric power steering system capable of balancing a steering assist force by correcting an offset and improving the steering feeling . a controller for an electric power steering system having motor driving means for driving a motor for electric power steering and motor current detecting means for detecting a current running through the motor is used in which the motor - driving means realizes a motor stop state in which no current runs through the motor under a non - energized state , uses a motor current detection signal under the motor stop state as the offset value of the motor current detecting means , and automatically corrects the offset of the motor current detecting means in accordance with the offset value .