A fill material 201 enclosed in an arc tube 201 with an inner diameter of 10.8 mm includes ScI3, argon, and mercury. A distance between electrodes 202 is set at 2.2 mm, and a distance between the inner wall of the arc tube 201 and the electrodes 202 is set at approximately 5.4 mm, which is approximately twice the distance between the electrodes 202. The lamp of the present invention is capable of forming thin arc and thereby achieving high luminance since only the metallic elements having an ionization potential of 6 eV or higher is contained in the fill material 207. The restriction of the short distance between the electrodes serves to stabilize arc. Scandium in the fill material serves to achieve a good color reproduction characteristic.