A short arc type mercury lamp structure has Hg and a rare gas which are enclosed inside a light-emitting tube. Kr is enclosed as the rare gas. It is possible to realize the initial intensity of radiation at the same level as in the case in which Ar is enclosed and prevent a sudden decrease in the intensity of radiation when the lamp is lighted for a long time. The longevity of the lamp is greatly increased than that of a lamp in which Ar is enclosed. The anode satisfies the formula: 1−r/(d0×tan θ)≧0.66, where r (mm) is the radius of the leading end surface of the anode, θ(°) is the angle between the electrode axis and the taper surface in the axial cross-section of the anode, and d0 (mm) is the inter-electrode distance.