PURPOSE: To prevent the fracture of an electrodeless discharge lamp due to a temperature rise by jointing a pair of symmetrical half-split annular glass tubes to each other at two positions to constitute an annular form.

CONSTITUTION: Cylindrical glass tubes as a pair are respectively curved, thereby forming a pair of half-split annular glass tubes 7 symmetrical with each other, and the tubes 7 are jointed to each other at two positions via thermal deposition or the like. Thus, an electrodeless discharge lamp 5 becomes annular via a pair of joint sections 8. In this way, the lamp 5 is formed out of the glass tubes 7 jointed to each other and, therefore, even when the temperature of the discharge lamp 5 rises due to lighting and the glass tubes 7 expand, the extent of the expansion is equal at the two joint sections 8. Thus, high stress due to the expansion does not occur at the joint sections 8. Furthermore, stress due to the expansion can be dispersed over the two joint sections 8, thereby preventing the occurrence of a fracture.