A method of manufacturing an arc tube for a discharge lamp unit, incorporating a primary pinch-sealing step for mounting an electrode assembly in an open end of a glass tube W with a chamber portion 12. The electrode assembly comprises an electrode rod 6, a connecting foil 7 and a lead wire 8 integrally connected in series. The electrode assembly is inserted into an open end of the glass tube W such that a leading end of the electrode rod projects into the chamber portion 12. A temporary pinch seal region L1 of the glass tube W is pinch-sealed such that a portion of the connecting foil that is connected to the lead wire is contacted by the glass tube W. A vacuum is maintained inside the glass tube and a main pinch seal region L2 of the glass tube is pinch-sealed such that a portion of the connecting foil connected to the electrode rod is contacted by the glass tube. When the main pinch seal region L2 of glass tube W is pinch-sealed, the negative pressure in the glass tube W is exerted on the softened sealed chamber portion 12 owing to supplied heat as well as the pressure exerted from the pincher 26b. Thus, the glass layer 15 is pressed against the surface of the molybdenum foil 7 so that hermetic contact is realized.