PURPOSE: To save energy by providing a pulse generator on a wheel to generate pulses having prescribed magnitude and number when a steering angle exceeds a certain given value such that a hydraulic motor is actuated.

CONSTITUTION: A disc 101 having slits 105 arranged in the circumferential direction is provided coaxially, and a light emitted from a light emitting element is transmitted intermittently to an optical detector via the slits 105 so that pulses proportional to a steering angular velocity are generated. The pulses generated are transferred to a control means 20 via a pulse interval detecting means 18. When a handle steering angle exceeds a prescribed value, an electromagnetic clutch 10 is turned on by a pulse signal to drive a pump 9, thereby allowing hydraulic fluid to be supplied to a power steering device.