In a rotary nozzle of the type attached to the bottom shell of a molten street vessel and designed so that a rotor having a sliding plate brick mounted thereon is rotated by a motor through a reducer and gearing to adjust the degree of opening of a nozzle bore and thereby to control the pouring rate of molten steel, the rotation of the rotor is effected by hydraulic cylinders in place of the reducer, gearing and motor. Thus, there is the effect of providing a rotary nozzle which is small in size, light in weight and low in cost.