Rhenium(I) biscarbonyl complexes with two phosphine ligands photocatalyzed not only CO2 reduction under CO2 atmosphere but also H2 evolution under Ar. The reductant 1-benzyl-1,4-dihydronicotinamide (BNAH) worked only as a one-electron donor, and it was quantitatively converted to its corresponding oxidized dimer (BNA2). The photocatalytic reactions required addition of a base such as triethanolamine, because deprotonation from the oxidized BNAH (BNAH•+) is essential for the suppression of the back electron transfer from the reduced rhenium(I) complex to BNAH•+. 1H, 13C, and 31P NMR studies under vacuum or 13CO2 atmosphere indicated that the rhenium(I) complex is relatively stable under the CO2 reduction conditions, but it is converted to some other complexes under the H2 evolution conditions.