Reduction of carbon dioxide is desired as an environmental problem of global warming. The study of generation of formic acid from carbon dioxide was performed under irradiation of ultra violet to photocatalyst. Ta2O5 could reduce carbon dioxide, but the band gap of Ta2O5 was 4.0 voltage. In this research, it was found that tantalum oxide / tantalum plate responds to visible radiation. Therefore, the reason of visible light response was examined. It was studied to make efficient tantalum oxide / tantalum plate.