PURPOSE: To provide the member, converting light into heat, which employs a half- mirror type carbon thin film on the inner wall thereof, by adhering the half-mirror type metallic thin film on the inner wall of a light transmitting hollow tube.

CONSTITUTION: Pyridine is vaporized from a material vessel 1, accommodating refined pyridine, by vacuum distillation and the particles of pyridine are transferred from one end of a quartz glass reaction tube 3 to the inside thereof through a feed tube 2 consisting of pyrex or the like. The temperature of a heating furnace 6 is increased to set the inside of the reaction tube 3 at the reaction temperature of about 950°C to decompose pyrolytically and form a carbon accumulated layer sequentially on the inner wall of the reaction tube 3. This carbon accumulated layer becomes a flat and smooth surface, having uniform thickness and provided with metallic luster on the surface thereof, and provided with a character of a half mirror. When fluid is flowed into the light transmitting hollow reaction tube and solar light or the like is projected against the reaction tube, the carbon thin film on the inner wall of the reaction tube heats the fluid by the effect of converting light into heat and whereby the temperature of the fluid may be risen as it flows through the reaction tube.