PURPOSE: To simplify structure by arranging a spool type servo-mechanism into the thick body part of a housing into which a stub shaft and an operating shaft are inserted and arranged.

CONSTITUTION: When a stub shaft 10 is turned by turn-operating a steering wheel, a torsion angle is generated on a torsion bar 11, and a relative turning displacement is generated between the stub shaft 10 and an operating shaft 12. Then, a relative turning displacement is generated also between the projection 29 formed onto the stub shaft 10 and the projection 31 formed onto the operating shaft 12, and the projection part 29 presses the inner surface of the spiral groove 28 formed onto a cylindrical member 27, and turns in the direction of the axis of the cylindrical member 28. Then, a pressing member 20 installed onto the cylindrical member 27 shifts in the axial direction, and a spool valve 14 is pressed by a valve operating arm 20a, and the steering hydraulic pressure can be controlled.