To provide a method for controlling the quantity of sucked liquid constant by selecting a rope of material generating strong capillary action between itself and inflammable liquid, and forming an imaginary liquid surface by binding the rope.

When carrying the inflammable liquid in a flask to a catalytic combustion burner, the material generating suction force with strong capillary action with the liquid is selected, and the rope is provided with the binding part. The imaginary liquid surface shown in the figure is formed at the binding part 2, and suction speed to the catalytic combustion burner is controlled to be constant regardless of the change of inflammable liquid level height 7 in the flask 5.