A floating member 41 floating near the liquid level L of a material M in a material tank 10 is descended as the height of the material liquid level L is decreased. The descending movement is converted into rotational movement of an outer cylinder portion in a double cylinder portion 51. The rotational movement automatically changes the size of a communication hole which is constituted by the overlaid portions of a through hole provided in an inner cylinder portion and a through hole provided in the outer cylinder portion in the double cylinder portion 51. This change can be optimized through the shapes of the through holes, which enables maintaining the ratio between the material M supplied from the material tank 10 to a cylinder portion 20 and air supplied from a vertical pipe 61 to the cylinder portion 20 at a constant value within a required range.
