Disclosed is a gas treatment device that can efficiently regulate the temperature of a gas without being affected by load. Said device is provided with: a compressor (1); a heat exchanger; a separator; an expander (3); a refrigerant gas flow control valve (22); a branching channel (13); a first branching-channel heat exchanger (24) and a second branching-channel heat exchanger (25); a first outlet channel that is connected to a liquefied process gas outlet on the separator and that bypasses the first branching-channel heat exchanger (24); a second outlet channel that is connected to an outlet on the expander (3) and that bypasses the second branching-channel heat exchanger (25); a first thermometer (23) in a main channel; a second thermometer (26) in the branching channel (13); a third thermometer (27) in the separator; a flow control valve (20) on the main channel; and a control means (5) that controls the flow control valve (20) and/or the refrigerant gas flow control valve (22) on the basis of temperatures measured by the first through third thermometers (23, 26, 27).