A gas decomposition device 100 includes one or two or more membrane electrode assemblies 5, each including a solid electrolyte layer 2, an anode layer 3 stacked on a first side of the solid electrolyte layer 2, and a cathode layer 4 stacked on a second side of the solid electrolyte layer; and porous current collectors 8a, 8b, and 8c including continuous pores 1b, the membrane electrode assemblies being stacked with the porous current collector, the solid electrolyte layer being composed of a proton-conducting solid electrolyte, the porous current collectors including porous metal bodies 1, each of the porous metal bodies 1 including an alloy layer 12a having corrosion resistance on at least a surface of the porous metal body 1 facing the continuous pores, and the porous metal bodies forming gas channels 9a, 9b, and 9c that supply gases to the anode layer and the cathode layer.