An intake-air cooling device is disposed on a rear-stage side of a pre-filter disposed on an intake-air inlet side of an intake-air duct for guiding intake air taken in from an intake-air inlet to a compressor, for cooling the intake air by spraying water to the intake air. The intake-air cooling device includes a plurality of nozzles configured to spray the water to the intake air, a plurality of water conduit pipes including the plurality of nozzles arranged in an axial direction of the plurality of water conduit pipes, and a plurality of supply pumps configured to supply the water to a corresponding one of the plurality of water conduit pipes. Each of the plurality of water conduit pipes is an endless member which has a different perimeter.