PURPOSE: To suppress the temperature rise of an infrared reflecting film, and to prevent the thermal deterioration of the infrared reflecting film, as well as the deterioration of an external tube by making the outer surface of an intermediate tube on which the infrared reflecting film is formed, abut on the inner surface of the external tube almost over the entire surface.
CONSTITUTION: An intermediate tube 10 is stored in an external tube 1, and, since the infrared reflected by an infrared reflecting film 11 pass through the tube, the temperature of the intermediate tube 10 is raised to a much higher level, even when it is suppressed not to reach no less than 500°. The outer surface of the intermediate tube 10 is made to abut on the inner surface of the external tube 1 almost over the entire surface, and the heat of the intermediate tube 10 is discharged to the outside through the wall of the external tube 1. The temperature rise of the intermediate tube 10 as well as of the infrared reflecting film 11 is thus suppressed. The thermal deterioration of the infrared reflecting film 1 is thus prevented, and the blackening of the external tube 1 can be prevented, because no sprashing is generated.
UCHIDA KAZUO
OKAMURA KAZUYOSHI
