A hydrocarbon generation system, comprising a co-electrolysis cell and a hydrocarbon generation cell, wherein the co-electrolysis cell is configured to generate carbon monoxide and hydrogen by abstracting oxygen from introduced carbon dioxide and water, the hydrocarbon generation cell is placed downstream of the co-electrolysis cell and is configured to generate hydrocarbon by introducing the carbon monoxide and the hydrogen generated in the co-electrolysis cell, each of the co-electrolysis cell and the hydrocarbon generation cell has an electrochemical reactor; the electrochemical reactor comprising: an oxygen-permeable electrolyte membrane, as well as a cathode and an anode disposed to either side of the electrolyte membrane, wherein the cathode is composed of an assembly; the assembly comprising an electrochemical catalyst and a conductive metal joined with each other to form an interface; and the electrochemical catalyst comprising: a metal oxide composed of one or two or more of zirconium oxide, cerium oxide, yttrium oxide, gadolinium oxide, samarium oxide, cobalt oxide and scandium oxide; and a metal variant, having a valence different from that of a metal composing the metal oxide; wherein the co-electrolysis cell and the hydrocarbon generation cell are each connected to an external power source to control the temperature of the electrochemical reactor and the surface potential of the electrochemical catalyst. wherein the co-electrolysis cell is configured to generate carbon monoxide and hydrogen by abstracting oxygen from introduced carbon dioxide and water, the hydrocarbon generation cell is placed downstream of the co-electrolysis cell and is configured to generate hydrocarbon by introducing the carbon monoxide and the hydrogen generated in the co-electrolysis cell, each of the co-electrolysis cell and the hydrocarbon generation cell has an electrochemical reactor; the electrochemical reactor comprising: an oxygen-permeable electrolyte membrane, as well as a cathode and an anode disposed to either side of the electrolyte membrane, wherein the cathode is composed of an assembly; the assembly comprising an electrochemical catalyst and a conductive metal joined with each other to form an interface; and the electrochemical catalyst comprising: a metal oxide composed of one or two or more of zirconium oxide, cerium oxide, yttrium oxide, gadolinium oxide, samarium oxide, cobalt oxide and scandium oxide; and a metal variant, having a valence different from that of a metal composing the metal oxide; an oxygen-permeable electrolyte membrane, as well as a cathode and an anode disposed to either side of the electrolyte membrane, wherein the cathode is composed of an assembly; the assembly comprising an electrochemical catalyst and a conductive metal joined with each other to form an interface; and the electrochemical catalyst comprising: a metal oxide composed of one or two or more of zirconium oxide, cerium oxide, yttrium oxide, gadolinium oxide, samarium oxide, cobalt oxide and scandium oxide; and a metal variant, having a valence different from that of a metal composing the metal oxide; a metal oxide composed of one or two or more of zirconium oxide, cerium oxide, yttrium oxide, gadolinium oxide, samarium oxide, cobalt oxide and scandium oxide; and a metal variant, having a valence different from that of a metal composing the metal oxide; wherein the co-electrolysis cell and the hydrocarbon generation cell are each connected to an external power source to control the temperature of the electrochemical reactor and the surface potential of the electrochemical catalyst. <EOS>