A light source device is provided with an LED having strong directivity, a reflective hood which has an interior reflecting surface for reflecting the illumination light from the light source, and a pair of first and second polarizing reflective plates for polarizing the illumination light from the LED in a specific direction. The first and second polarizing reflective plates have a specific length and width, and a back surface formed from a high reflectance plate. The light source is secured to the reflective hood. A specific interval is provided between the first and second polarizing reflective plates and the reflecting surface of the reflective hood, and a specific interval is provided between the two plates with the optical axis passing through the 0° direction angle of the light source in between.