A gas cooler (10) which is provided with a heat exchanger (6), cools a gas to be cooled, which is introduced from the outside, by performing heat exchange between the gas to be cooled and the heat exchanger, and discharges the cooled gas to the outside. The heat exchanger includes: a plurality of heat transfer fins (8) which are placed side by side via a prescribed gap therebetween, the gas to be cooled flowing through the gaps; and heat transfer tubes (7) which pierce through the plurality of heat transfer fins and are provided in a plurality of rows along the direction in which the gas to be cooled flows. The outside diameter do of the heat transfer tubes is 20 to 30 mm.