An arc tube is formed by a glass tube that is turned at a substantially middle thereof and wound around a spiral axis from the middle, to have a double-spiral structure. End portions of the arc tub are wound around the spiral axis. A holder has insertion openings formed therein in such shapes that correspond to shapes of the ends of the arc tube. The insertion openings allow the ends of the arc tube to be inserted along a bottom wall of the holder. The holder also includes guide grooves provided in the areas before the insertion openings in the spiral direction of the ends of the arc tube. The guide grooves allow the end portions of the arc tube to come in contact, and when the arc tube is rotated around the axis, guide the ends of the arc tube to the insertion openings.