PURPOSE: To manufacture a controlling device of radiant heat, improving radiant capacity and setting up a gap accurately by a method wherein the surface of contact plate opposing to radiant plate is formed into concavity.

CONSTITUTION: The central part of a contact plate 9a is formed into concavity. Said cantral part is bent by vapor pressure of working fluid 13 in a container 7 but the gap between a radiant plate 6 and a contact plate 9a may be set up accurately by a spring 11 since said plate 6 comes into contact with the periphery of said plate 9a. On the other hand, while the heat conductance from said plate 9a to said plate 6 is similar to that of a flat plate, the temperature distribution A on said plate 6 is made more even than the conventional distribution B due to the formation of concavity to raise the mean temperature improving the heat conductive efficiency.