PURPOSE: To improve workability in the case where an electric heater is replaced with new one, by a method wherein one end side of a heat-pipe and the heater are held between heat-transferring blocks, which can be divided into two parts, and they are integrally formed as one body.

CONSTITUTION: A liquid medium in a heating part 9a of a heat-pipe 9 is heated by an electric heater 11, is vaporized, and takes the heat from the heater 11 as the latent heat of vaporization. After that, its vapor is moved to a heat-emitting part 9b of the heat-pipe 9 laid down in a road bed, the latent heat of condensation is emitted in the road bed, snow on the road bed is allowed to melt and it is prevented from freezing. Since the heater 11 is in contact with the heat-pipe 9 through heat-transferring blocks 12, which can be divided into two parts, the heater 11 is taken out by loosening clamping bolts 13 and is replaced with new one when the heater 11 malfunctions. If the need arises, the heat-pipe 9 is formed in looped shape or the diameter of the heating part 9a is made larger, and thus a large amount of heat is transferred. In this way, since the heater 11 can be taken out by shifting laterally, the heater 11 can be removably mounted even in a narrow space when replaced with new one. In addition, the cost of construction can be reduced and a performance can be improved by the reform of the heater.