PURPOSE: To prevent any separation of phosphor, which might be caused during insertion of a discharge-path restricting body, by providing a bulb with connection grooves, and fitting the sides of the said restricting body into the said grooves.

CONSTITUTION: Discharge-path-restricting-body receiving parts 11, which are opposed to one another and extend in the direction along the length of the bulb 1, are provided on the outer side of a bulb 1. The inner side of the part 11 is provided with a connection groove 12, which opens to the inside of the bulb 1 and the depth of which gradually decreases as it comes near to the top of the bulb 1. Since the connection groove 12 of the part 11 has a slant shape which corresponds to the slant shape of side parts 41 of a discharge-path restricting body 4, insertion of the body 4 into the bulb 1 is completed when the side end surfaces of the body 4 become in contact with the bottoms of the grooves 41.