An electric discharge lamp has a ceramic luminous tube 5 and filled with xenon gas, a pair of electrodes 9, 10 held by the ceramic luminous tube, and a glass outer tube 6 accommodating the ceramic luminous tube and the pair of electrodes. The ceramic luminous tube includes a luminous portion 7 emitting light by electric discharge, and a pair of small diameter tube portions 8, 8 respectively connected to both end portions of the luminous portion in a longitudinal direction. Value of P/(r•t) is not less than 4.8 and not more than 32, where P (atm) is pressure of xenon gas filled into the ceramic luminous tube, r (mm) is an inner diameter of the luminous portion of the ceramic luminous tube, and t (mm) is thickness of the luminous portion of the ceramic luminous tube.