PURPOSE: To elevate the temperature of the coldest part of a lamp and to improve the color rendering property by protruding a projection of a metal end cap which is for sealing a transparent alumina tube towards the inside of the tube, and fixing electrode parts on the projection.

CONSTITUTION: An end cap 11 which is to seal a high pressure sodium lamp such as a transparent alumina tube 13 etc., is formed providing a first step 12a and second step 12b. The first step 12a is inserted into the alumina tube 13 and fixed with glass solder 14, while an electrode 15 is fixed on the projection 18 of the step 12b so that the electrode 15 extends to the inner direction. Thus the hottest part, that is the electrode 15, positions near the coldest part and the temperature of the coldest part is elevated, and the color rendering property can be improved without providing any special thermal insulator on the tube end.