There are many studies on the electrochemical reduction of CO2 on a Cu foil electrode. However, one of most serious problems in a practical use of this process is that this electrode loses its catalytic activity for the reduction of CO2 to hydrocarbons owing to the deposition of poisoning species in a short time after the start of electrolysis. In the present study, the reduction of CO2 has been performed at the three-phase (gas \ liquid \ solid) (GLS) interface on a Cu net electrode. In this electrode system, CO2 is supplied to the electrode surface from the gas phase, and a high concentration of CO2 can be maintained even in acidic solution. The poisoning process was extremely suppressed at the GLS-Cu electrode in a long-term electrolysis, and the main products obtained with this electrode were CO2 C2H4 and CH4.