Disclosed is a novel photosensitizer that can absorb light in a wide visible light region and in the case of a very thin film form, can enhance a light absorption efficiency by virtue of a large light absorption coefficient. The photosensitizer is used for metal oxide semiconductor electrodes and comprises a metal complex represented by a general formula ML1L2X2, wherein M is a group 8 transition metal of the periodic table, Xs are each independently a halogen atom, a cyano group, a thiocyanate group, an isothiocyanate group, an isocyanate group, an isocyanide group or a hydroxyl group, or a bidentate ligand in the case where Xs are bonded to one another, L1 and L2 are each a ligand having an aromatic ring, and either L1 or L2 has a functional group having a COOH group or PO(OH)2, and when the photosensitizer is adsorbed on a metal oxide semiconductor electrode via ligands L1 and L2, the difference ΔL between the energy levels of ligands L1 and L2 in their excited states, calculated in accordance with a GAUSSIAN03 quantum chemistry calculation program is 0.25 eV or more.