In a gas discharge tube, a first discharge path-induction portion is arranged between a first discharge path-limit portion and a second discharge path-limit portion. A voltage is applied to the first discharge path-induction portion from the outside. As a result, an active starting discharge capable of passing through a first opening of the first discharge path-limit portion is produced between a cathode portion and the first discharge path-induction portion. As a consequence, there is facilitated the discharge at a starting time to pass through a second opening. As a consequence, there is achieved a rapid starting of discharge between the cathode portion and an anode portion. Therefore, in order to achieve further enhancement of brightness, there can be carried out with ease a further miniaturization pertaining to the openings, in terms of its area size, of the discharge path-limit portion while the starting properties being kept excellent, without any increase in a voltage at the starting time of the lamp so much.