A photopolymerization device (20) has: a workpiece holding part (1) that holds a workpiece (W); and a photoirradiation device (6) that is arranged above the workpiece holding part (1) and that radiates light toward the workpiece (W). The photopolymerization device (20) is configured such that a reflecting plate (3) that has a reflecting surface that has a specular gloss at angles of 60° of 10-200 is arranged below the workpiece holding part (1) and such that light that arrives at the reflecting surface of the reflecting plate (3) is radiated toward the workpiece (W).