To provide a short arc type mercury lamp which has suppressed evaporation of an electrode substance at the tip of a cathode without forming a cathode spot at the tip of the cathode at starting and has shortened the time till transition to stable lighting.

The short arc type mercury lamp SHL is equipped with an airtight container 1 of ultraviolet transmissivity, a cathode 2K that has a cathode main part K1 positioned at the tip, an axis K2 to support the cathode main part, and a coil Ck that contains an electron emitting substance installed at the axis at the position retreated to the base side from the cathode main part and is installed in the airtight container, an anode 2A that is installed in the airtight container separated and opposed to the cathode with a small spacing, and a discharge medium containing mercury and rare gas. When the distance between the tip of the coil of the cathode and the tip of the anode is made L1, and the distance between the electrodes is made L2, the formula 1:1COPYRIGHT: (C)2008,JPO&INPIT