The disclosure relates to a discharge lamp including a light emitting tube having a discharge space therein, and a pair of electrodes disposed in the discharge space so as to be opposed to each other, wherein a changing rate of a cross-sectional area is equal to or lower than 200%. The changing rate is a rate of change of the cross-sectional area in every 0.25 mm in a direction along an optical axis of the light emitting tube. The cross-sectional area is an area of a plane perpendicular to the optical axis in a space between an outside shape of at least one of the pair of electrodes and an inside wall of the light emitting tube.

A discharge lamp includes a cathode in a luminous tube, and an emitter, other than thorium, is added to the cathode. The emitter is prevented from being excessively vaporized from the cathode and depleted soon. Smooth lighting is enabled even at start-up. A main body part (31) of the cathode (3) is made from a metallic material having a high melting point and containing no thorium. A front end (32) is made from a metallic material having a high melting point and containing an emitter (excepting thorium). Inside a sealed space (33) formed in the main body part (31) and/or the front end part (32) is received a sintered compact (34) containing an emitter (excepting thorium) that is higher in concentration than the emitter contained in the front end part (32).

A discharge lamp includes a cathode in a luminous tube, and an emitter, other than thorium, is added to the cathode. The emitter is prevented from being excessively vaporized from the cathode and depleted soon. Smooth lighting is enabled even at start-up. A main body part (31) of the cathode (3) is made from a metallic material having a high melting point and containing no thorium. A front end (32) is made from a metallic material having a high melting point and containing an emitter (excepting thorium). Inside a sealed space (33) formed in the main body part (31) and/or the front end part (32) is received a sintered compact (34) containing an emitter (excepting thorium) that is higher in concentration than the emitter contained in the front end part (32).