A light source device includes a light source lamp, a rotary plate, a heat absorbing portion, and a filter mounting member. The light source lamp emits illumination light. The rotary plate includes multiple opening portions that are selectively disposed in the illumination light path of the light source lamp. A reflective filter that reflects light of a wavelength that acts a heat source in illumination light is provided in one of the multiple opening portions of the rotary plate. The heat absorbing portion absorbs heat included in reflected light reflected by the reflective filter in the opening portion. The filter mounting member disposes the reflective filter in the opening portion at a predetermined angle of inclination to the optical axis of the illumination light. By disposing the inclined reflective filter in the illumination light path, reflected light reflected by the reflective filter is reflected towards the heat absorbing portion.