PURPOSE: To prevent amalgam from having an excessive temperature rise by providing a fluorescent lamp with a thermally-actuated member deformed by high surrounding temperature at the time of stabilized lighting, etc., and keeping a heater away from a thin tube.

CONSTITUTION: A fluorescent lamp 20 is connected to a power supply by fitting a base 2 on a socket (not illustrated) and is lighted through a high frequency lighting circuit part 10 housed in a cover 1. When a stabilized lighting state is reached, the fluorescent lamp 20 and the lighting circuit part 10 are so heated as to make a temperature rise of the gap 8 between a lamp support plate 7 and a circuit substrate 9, giving a thermal deformation to a thermally-actuated piece 6 and keeping a heater 3 nearer to a thin tube 23 so as to cover the tip part of the thin tube 23 with a recess part 5 formed on a heat radiating member 3. As a result, the heat of the thin tube 23 is conducted to the heat radiating member 3 and radiated from heat radiating fins 4... which are formed on the heat radiating member 3. Consequently, the thin tube 23 is not subjected to temperature rise, while the amalgam 24 housed in the thin tube 23 also does not rise in temperature rise and is prevented from melting as to keep an optimum operation temperature, to improve luminous efficacy and stabilize a light flux.