To provide a short arc discharge lamp having less consumption of an electrode due to a shortened arc, suppressing crystallization in the upper wall surface of an arc tube and having excellent optical characteristics, high brightness, high efficiency and long life by defining dimensions of the light emitting part of a quartz arc tube and to provide a light source device used therewith.

This short arc discharge lamp for horizontal lightning has a quartz arc tube wherein a pair of electrodes is sealedly attached to both ends thereof, at least a mercury and a rare gas are sealed inside and the distance between the electrodes is 0.5-2.5 mm, inclusive. In this case, where the distance between the shaft of the electrode and the maximum diameter on the upper side in the vertical direction of a light emitting part of the quartz arc tube is D1 and the distance between the shaft of the electrode and the maximum diameter on the upper side in the vertical direction of the light emitting part of the quartz arc tube is D2, it is defined by an equation 1.1≤D1/D2≤2.0; and where the horizontal length L in the tube axial direction of the arc tube is defined by an equation L 2≤L/D2≤5.