The phenomenon of "Singing Flame" or "Gauze Tone" is the vibration of an air-column in a tube excited by heat supply. As the temperature of the airflow changes at the hot heater in adverse phase to the air velocity variation, there occurs some phase lag in the airflow when passing through the heater. Then, according as the phase of the velocity variation at the heater is by a quarter period before or after the phase of the pressure variation, the vibration is encouraged or discouraged. The characteristic that according to its position the heater can be an exciting source or a damping source to the vibration, is thus explained.