The injection type nozzle of the present injection is a two-fluid pressure nozzle comprising a centrifugal pressure nozzle for spraying a feed liquid and a cylindrical pipe for blowing out a high-speed gas, provided around the centrifugal pressure nozzle, said two-fluid pressure nozzle having a tapered structure at the front end portion and said cylindrical pipe for blowing out a high-speed gas, having air-purging through-holes at the front end portion. The spray dryer of the present invention comprises a drying chamber, the above two-fluid pressure nozzle provided at the bottom of the drying chamber with the nozzle tip directed upward, an inlet for feeding a hot gas into the drying chamber, and an outlet for driving an exhaust gas out of the drying chamber. The spray dryer employing a closed system according to the present invention comprises a drying chamber, the above two-fluid pressure nozzle provided at the bottom or top of the drying chamber with the nozzle tip directed upward or downward, an inlet for feeding a hot gas into the drying chamber, and an outlet for driving an exhaust gas out of the drying chamber, in which spray dryer the hot gas for drying fed into the drying chamber and/or the high-speed gas for atomization is fed by circulating the whole or part of the exhaust gas after spray drying. In the two-fluid pressure nozzle of the present invention, diameters of droplets formed can be controlled by controlling the flow speed of the high-speed gas for atomization.