The invention is directed to preventing occurrence of molybdenum foil breakage during a pinch sealing operation in a method of fabricating an arc tube having a pair of molybdenum foils pinch-sealed on both sides of a spherical portion of a glass tube by sequentially pinch-sealing the respective molybdenum foils. A first molybdenum foil is not pinch-sealed (first pinch seal) with an inert gas introduced into a glass tube as in a conventional embodiment, but is pinch-sealed with the internal pressure of the glass tube maintained at a vacuum of 0.5 torr or less. As a result, oxidation of the molybdenum foils causing breakage of the molybdenum foils during a pinch sealing operation is minimized. Hence, an arc tube having each of a pair of molybdenum foils made of molybdenum whose purity is 99.95% or more and with a thickness of 20 .mu.m or less can be fabricated.