In a fluorescer solution, a plurality of types of fluorescent particles are contained in a resin liquid. Average particle sizes of these fluorescent particles decrease as densities of the types increase. In other words, average settling rates vs of the types of the fluorescent particles ascertained by v s = D p 2 × ( ρ p - ρ f ) × g 18 × η are equal to each other, where Dp is an average particle size of each of the types of fluorescent particles, pp is a density of each of the types of fluorescent particles, pf is a density of the resin liquid, η is a viscosity of the resin liquid, g is the acceleration due to gravity, and vs is an average settling rate of each of the types of fluorescent particles.