PURPOSE: To utilize the frictional heat of air as a heat source, by providing an open-air introducing mechanism and a pressure-reduced, frictional heat generating mechanism for discharging heated air in an enclosed chamber.

CONSTITUTION: An open-air introducing mechanism 26 having an automatically operated valve 27 is provided at a lower portion of an enclosed, hollow heat generating chamber 1 which is charged with a heat accumulating medium, and a pressure-reduced, frictional heat generating mechanism X having a suction port 4 is fitted at a proper position in the outer wall of the chamber 1. The frictional heat generating mechanism X includes rotor blades 6 driven by a motor 5 surrounded by a hollow space 24, which rotor blades 6 constitute a frictional heat generating section A, and it has an outlet port 25 from which heated air is discharged. Further, on the suction side of the rotor blades 6, a driven mechanism Y, which is turned by the effect of viscosity of gas along with rotation of the rotor blades 6, is constituted by forming a turbine wheel 7 with a ring 12 having vanes at its peripheral portion and providing rotor blades 8 connected to the turbine wheel 7 by a shaft 11.