A hot-air supplying method that includes: generating, by means of a heat pump, hot air that is at a temperature lower than a desired target hot-air temperature; subsequently heating, by a heater, the hot air having been generated by the heat pump, while controlling the heater the temperature adjuster so as to adjust the temperature of hot air thus heated to the target hot-air temperature. This makes it possible to supply, with reduced energy loss and at low costs, hot air for processing a work, the hot air being necessary in a factory where processing and assembly or the like are carried out. Further, temperature control accuracy is enhanced.