PURPOSE: To always stably maintain luminescent color produced by a metal halide lamp by providing an air regulating plate for regulating cooling air quantity for a metal halide lamp.

CONSTITUTION: Cooling air from a blower 12 is blown out from an air supply outlet 16, and then flows toward a metal halide lamp 5 through a guide plate 13, so that the lamp 5 is cooled. In this case, the air quantity for cooling the lamp 5 is regulated by an air regulating plate 21. For example, when emission color of the lamp 5 is reddish, cooling air quantity is increased so that the temperature of the lamp 5 is lowered, and thus the color becomes close to a white light. Then, when emission color is bluish, cooling air quantity is decreased so that the temperature of the lamp 5 is raised, and thus the color becomes close to a white light. Accordingly, the luminescent color due to fluctuation of sealed iodide metal at the time of manufacturing a lamp 5 is regulated closed to white.