To provide a mercury-free arc tube for a discharge lamp device achieving low power consumption and having characteristics similar to those of a mercury-free arc tube of a prior application.

The mercury-free arc tube comprises an airtight glass bulb 12 sandwiched between pinch seal parts 13a and 13b, and a pair of electrodes 15a and 15b opposed to each other in the bulb 12. A metal halide for main light emitting, a metal halide for auxiliary light emitting, and a rare gas for startup are sealed into the bulb 12. An inner diameter of the bulb 12 at a center position between the electrodes is set to 1.5 to 2.7 mm, the distance between the electrodes is set to 1.0 to 4.0 mm, and the protruding length of the electrodes toward the inside of the bulb 12 is set to 0.3 to 1.8 mm, thereby achieving a stable discharge at a low power of 15 to 30 W. Since the sealing pressure of the rare gas for startup is high (8 to 20 atmospheres), the vapor pressure of the metal halides is raised, so that the light flux increases and the tube voltage increases, too. The bulb 12 is small, which reduces heat radiation quantity and maintains the electrode temperatures high. This causes no rise of the re-ignition voltage of the bulb and no flicker of the arc. The sealing quantity of the metal halides is defined. This provides luminescence with substantially the same chromaticity as that for a mercury-containing arc tube or a mercury-free arc tube of the prior application.