Provided is a gas cooler for cooling a produced gas on a side from which the produced gas exits, the produced gas being produced by partially oxidizing and gasifying a carbon-containing fuel in a gasification furnace inside a pressure vessel. A distance (SL) between tubes of a tube bundle of a heat exchanger provided inside the gas cooler is set such that the tubes are in contact with each other or adjacent to each other in a gas-flow direction of the produced gas. Since the tubes are in contact with each other or adjacent to each other, a particle flowing with the gas flow is only deposited as a deposited particle in a concave portion between the tubes, whereby the decrease in heat exchange efficiency caused by particle deposition can be suppressed.