PURPOSE: To make atomized particle size fine and uniform as well as to equalize a spray amount, by forming a spray port having no extremely narrow part except both end sides and average opening width by two simple notch parts.

CONSTITUTION: To the inner bottom part of a bottomed cylindrical nozzle main body 8, a curved inner peripheral surface 8a almost coaxial to the central axis core P of the main body is formed and notch parts 10, 10 for forming a spray port 7 are provided to the bottom part side of the main body 8 as well as at least one part of flange parts of the notch parts 10, 10 positioned to the side of the axis core P is made narrow toward the axis core side in bottom surface view of the main body 8 as well as notch parts 10, 10 are made wide toward the leading end of the main body 8 in side surface view of the main body 8 so as to atomize and inject a gas-liquid mixture from the spray port 7 in a sector pattern. In the bottom surface view of the main body 8, corner parts (b), (b) of notch flange part at a position close to the axis core P are offset to mutually opposed sides respectively against a surface S1 passing the axis core P and a surface S2 passing the axis core P as well as crossing the surface S1 at right angles.