To make a sound and vibration countermeasure at the time of a large steering load of a rotary type control valve and steering responsibility at the time of low load steering compatible with each other by a groove which can be processed at low cost.

A communicating degree of a groove 2a and a groove 1a of a valve body is increased at the time of left steering when the oiling groove 1a runs left, a communicating degree with a drain groove 1b is lowered, assist hydraulic pressure is supplied to one power cylinder chamber from the groove 2a, simultaneously the groove 2b communicated to the other power cylinder chamber comes to be in a non- pressure state as a communicating degree with a drain groove 1c is increased, and a power cylinder assists left steering. The assist hydraulic pressure reaches an inner periphery of a ring 4 from a groove 1d. As left running of the grooves 1a, 1g is large at the time of a large steering load, the groove 1g is removed from the groove 2b and blocked by a valve body inner peripheral surface, the ring 4 carries out a sound and vibration countermeasure by giving resistance to rotation of a shaft 1 by friction by hydraulic pressure to the inner periphery. The groove 1g is communicated to the groove 2b, drains inner peripheral pressure of the ring 4 and prevents lowering of steering responsibility at the time of low load steering.