This invention relates to a heat generating device and its applied warming or drying system which utilizes the air friction heat generated within a sealed chamber at reduced balanced pressure. This device comprises at least two of the sealed chamber connected in series, and a control means for reducing the current supplied to a rotary means of the sealed chamber when the reduced balanced pressure is achieved in the chamber. The device further comprises a connecting chamber with a plurality of heated air discharging slits for connecting the outlet of the preceding sealed chamber in air flow and the following sealed chamber, and/or an opening degree adjusting member for reducing the inlet opening of the sealed chamber when the reduced balanced pressure is achieved, thereby improving heating efficiency and saving energy.