Provided is a photopolymerization initiator including (a) a photosensitizer, (b) a tertiary amine compound, and (c) an aryl iodonium salt, wherein the photopolymerization initiator is characterized in that an aryl iodonium salt that generates an acid having a dissociation constant of -3.0 or higher in 25°C water is selected as the aryl iodonium salt (c).