A method for operating a clothes treating apparatus comprising a hot air supplying unit provided with a heater and a blowing device, and having a drying function of drying clothes by supplying hot air into a drum by use of the hot air supplying unit, includes rotating the drum with the clothes introduced therein, and supplying hot air into the drum by using the heater and the blowing device while the drum is rotated, wherein an air flow rate supplied by the blowing device changes during the hot air supplying step.