The carbon dioxide reducing method using light includes: (a) preparing a carbon dioxide reducing cell including: a cathode chamber that holds first electrolytic solution containing carbon dioxide; an anode chamber that holds second electrolytic solution; a proton exchange membrane inserted between the cathode and anode chambers; a cathode set inside the cathode chamber to contact the first electrolytic solution, and the cathode having copper, gold, silver, indium, etc. on the cathode; and an anode set inside the anode chamber to contact the second electrolytic solution, the anode having first semiconductor layer constituted by nitride semiconductor including AlxGa1-xN layer wherein 0≦x≦0.25, an n-type GaN layer, and second semiconductor layer constituted by semiconductor having pn junction structure and electrically connected to the first semiconductor layer through p-type semiconductor layer, further to the cathode through no external power source; and (b) irradiating the anode with light to reduce carbon dioxide on the cathode.