Abstract: Provided are: a photoacid generator that effectively generates acid even when a substance such as a colorant which attenuates or blocks radiated light is present at a high concentration, the film thickness thereof is large, and a light source is visible light to infrared light, particularly infrared light having low energy; and a highly curable photosensitive composition using the photoacid generator. The present invention is a photoacid generator that is a metal complex having, as a ligand, a ring structure formed by bonding five-membered ring aromatic heterocyclic compounds directly or by ?-conjugation, wherein a central metal has one or two axial ligands, and the axial ligand has an onium salt structure.