A discharge lamp (10) has a fixing base (20) on one end. In some embodiments, the fixing base comprises a cylindrical first body portion (21) having a pair of notches (21H), a cylindrical second body portion being larger than the diameter of the first body portion and having a joint (23H), and a groove portion (25) formed in between the first and second body portion and having an equal or less diameter of a space of the pair of notches. A first body portion and a stepped surface (21B) of the groove portion is contacted to a base surface of a lamp holder (50) when the fixing base is inserted to the lamp holder.