A mercury free arc tube for a discharge lamp has a closed chamber filled with rare gas and a metal halide containing at least Na halide, Sc halide and In halide, and electrodes. A ratio of a filled amount of the In halide to a total filled amount of metal halide is ranging from 0.1 to 2.0 wt %. When the ratio of the charging amount of InI is 0.1 wt % or more, the chromaticity x, y of a luminescent color during a stable discharge falls within a chromaticity standard range A of white light source. When the ratio of charging amount of InI is 2.0 w % or less, a chromaticity y minimal value of luminescence of the arc tube at the transient time is 0.29 or more, whereby purplish red color is less conspicuous and there is no fear that an emission of the arc tube is misidentified a red marker lamp.