In an arc tube for discharge lamp, an electrode assembly is formed by integrally joining an electrode rod, a molybdenum foil, and a molybdenum lead wire. The electrode assembly is sealed into pinch seal portions located at both ends of a glass tube. The electrode assembly, before being pinch-sealed into the pinch seal portions, receives vacuum heat treatment at 200 to 800.degree. C. Hereby, the water content of the assembly is adjusted to 10 ppm or less, and desirably to 3 ppm less and an oxide film attached to the surface of the electrode assembly is removed. Therefore, the quantity of impurity (water or gas) enclosed in the closed glass bulb is very small, so that it is possible to provide an arc tube in which the flicker is not produced, luminous flux of 3000 lm or more is obtained, and starting voltage can be lowered to about 15 kV.