A method of manufacturing a gas discharge tube by closing an opening of a glass tube by forming a glass layer with outer peripheral shape identical to the outer peripheral shape of the glass tube on an end face of the glass tube. An open end face (opening) of the glass tube is pressure-welded to a dry film containing a low melting point glass powder and a binder resin, and then the glass tube is lifted up to transfer the dry film for closing the opening to the end face of the glass tube. A phosphor support member is inserted into the glass tube from a side opposite to the end face and then an end of the phosphor support member is caused to adhere to the dry film. The binder resin is burnt off, and the dry film is vitrified to produce a low melting point glass layer.