A photosynthesis apparatus includes a groove part formed in a semiconductor substrate; a first conductive type area formed on one side surface of the groove part; a second conductive type area formed on another side surface of the groove part; an oxidation electrode formed in contact with the first conductive type area on the one side surface; a reduction electrode formed in contact with the second conductive type area on the other side surface; and a proton diaphragm formed at a center part of the groove part. Water including carbon dioxide is supplied to the groove part, and light is radiated to the oxidation electrode or the reduction electrode to generate oxygen and a hydrogen ion from the water at the oxidation electrode, and the generated hydrogen ion penetrates the proton diaphragm and reacts with the carbon dioxide to generate formic acid at the reduction electrode.
