PURPOSE: To bring a capillary to a huge state in the piping of a heat-insulating section, and to bring a heat transfer distance to the huge state by communicating a pipe for a vapor path and a channel pipe with a cavity section in a housing while vertically forming a space and moving a working fluid by the pressure difference of atmospheric pressure in the cavity section and a condensing section by the evaporation of the working fluid.

CONSTITUTION: Heat generated in a coil 5 for the stator 4 of a motor l is transmitted over a cavity section 11 through the inner circumferential wall 3a of a housing 3, and the working fluid of a first wick 23 is evaporated in the cavity section 11. Pressure difference is generated in atmospheric pressure in the cavity section 11 and a condensing section 15 by the evaporation, the vapor of the working fluid is moved at high speed from the cavity section 11 in the housing 3 into the condensing section 15 through a pipe 12 for a vapor path, vapor latent heat is discharged through the condensing section 15 and the working fluid is condensed, and the heat of the motor 1 is discharged to the outside. The working fluid liquefied by condensation is flowed back to the first wick 23 in the cavity section 11 of the housing 3 through a channel pipe 13.