The reduction in CO2 emissions by photoelectrochemical conversion of the CO2 to formic acid and methanol using silicate rock (andesite) powders suspended in water is presented. For photoelectrochemical reduction of CO2, a homemade cell with a platinum and a copper electrode was used. 0.1 M KHCO3 solution was used as the electrolyte. In the photoelectrochemical reduction of CO2 with a copper cathode in the catholyte dispersing andesite powder, mainly formic acid, methanol, methane, ethylene, carbon monoxide, and hydrogen were produced. Consequently, it was found that this method using a copper electrode was effective for formic acid and methanol formations from carbon dioxide.