To reduce on-vehicle time occupied space, to increase the freedom of on-vehicle layout and to appropriately transmit rotation by integrating a hydraulic control valve with a torque transmission direction changing means provided at an intermediate part of a steering shaft system.

A steering shaft system is provided with a hydraulic control valve 11 based on a rotary passage selector valve 26 for controlling driving of a power cylinder, and a torque transmission direction changing means 12 provided at an intermediate part of the steering shaft system. A valve body 21 of the hydraulic control valve 11 is integrally connected to a gear body 41 of the torque transmission direction changing means 12. A transmission shaft 23 connected to an input shaft 22 on the steering wheel side through the rotary passage selector valve 26 is extended toward the gear body 41 while piercing the valve body 21 so as to face an output shaft rotatably journalled to the gear body, from an almost orthogonal direction of axes, and both shafts are gear-connected by gear connecting means 50, 51 in the internal space. The output shaft is journalled movably in the axial direction, and adjusting mechanism 40 is provided to adjust the axial moving quantity of the output shaft.