In an atomizer constructed to cool inlet air for a gas turbine by spraying fine droplets of water into the inlet air, a spray nozzle is disposed to spray the finely atomized droplets of water from an outer edge of an atomized airstream into a high-speed zone thereof, towards a central region of the airstream. The atomized airstream meets an airstream of a low-speed zone formed at a downstream side, and after the two kinds of airstreams have been mixed and unified, this mixture is supplied to an axisymmetric compressor. Devices such as a feed water pipe and spray nozzle are placed in the low-speed zone so as not to obstruct the airstream.