An internal part for a lighting tool for a vehicle, including: an entering portion for light; an emitting portion for light; and a light-guiding portion to guide the light from the entering portion to the emitting portion, the part being arranged at a distance of 5 mm or less from a light source, wherein the part is a molded body formed of a resin composition, wherein a 5-millimeter thick plate, obtained by subjecting the resin composition to injection molding at a cylinder temperature of 260° C., a die temperature of 80° C., a cycle time of 50 seconds, and a retention time of 230 seconds, a total light transmittance of 80% or more, and a ratio (X/Y) of a spectral light transmittance (X) of the 5-millimeter thick plate at a wavelength of 350 nm to a spectral light transmittance (Y) thereof at a wavelength of 400 nm is 0.75 or more.