A light source device comprising a filament showing high electric power-to-visible light conversion efficiency is provided. A light source device comprising a translucent gastight container, a filament disposed in the translucent gastight container, and a lead wire for supplying an electric current to the filament is provided. The filament comprises a substrate formed from a metal material and a visible light reflectance-reducing film coating the substrate for reducing visible light reflectance of the substrate. The reflectance of the substrate for visible lights is thereby made low, and the reflectance of the substrate for infrared lights is thereby made high. Therefore, radiation of infrared lights is suppressed, and visible luminous efficiency can be enhanced.