PURPOSE: To prevent the freezing of a door by providing the guide rail of a sliding door at the entrance in contact with outside air, integrally with heat mechanism from a heat pipe extended along the guide rail so as to heat the guide rail at the time of intense cold.

CONSTITUTION: A guide rail 1 for the guide protrusion 25 of a sliding door 24 is formed by bending a plate 2. A heat pipe 4 provided with an electric cassette heater 9 or the like is provided along a guide groove 3, and cement mortar 5 or the like is filled inside. A small quantity of operating liquid such as alcohol is filled in a pipe 6 to create a vacuum. Wiring and piping work is dispensed with, and heating can be performed with little electric power. Freezing at the time of intense cold can thereby be prevented efficiently.