PURPOSE: To make the heat pipe small, by equalizing a volume of a working liquid to be sealed in a heat pipe elemental pipe with that of a space defined by two spaced valves provided onto a soft tube that constitutes part of a delivery pipe, and by collapsing said tube under the influence of the atmosphere thereby injecting said volume of the working liquid contained in said space into the heat pipe elemental pipe.

CONSTITUTION: A working liquid tank 2 and the heat pipe elemental pipe 3 are connected through the delivery pipe 4 whose middle part comprises the soft tube 6. Onto the soft tube 6 are attached the two forceps 9a, 9b such that the volume of the delivery pipe defined between said forceps is equal to the volume of the working liquid to be sealed in the heat pipe elemental pipe 3. After the heat pipe elemental pipe 3 is evacuated by a vaccum pump 8, the forceps 9b adjacent the heat pipe elemental pipe 3 is closed, and the forceps 9a adjacent the working liquid tank 2 is opened to retain the desired volume of the working liquid in the space between the forceps 9a, 9b. Then the forceps 9b adjacent the heat pipe elemental pipe 3 is opened to inject the working liquid into the heat pipe elemental pipe 3.