PURPOSE: To stably and sufficiently dissolve required gas in a liquid by extinguishing a large number of gas bubbles contained in the gas mixed solution sent out of a mixing and stirring apparatus for mixing gas with the liquid under stirring.

CONSTITUTION: An air bubble extinguishing apparatus 1 is connected to a mixing and stirring apparatus 3 in a liquidtight state at one end part thereof and formed into a coil shape wherein a plastic pipe 1A is spirally turned about six times. The other end part of the gas bubble extinguishing apparatus 1 is connected to an air bubble extinguished water using apparatus 2 using an aqueous solution free from air bubbles. By this constitution, a large number of the air bubbles in the air mixed aqueous solution are extinguished by the actions of a fluid magnetic field and centrifugal force in a process wherein the air mixed aqueous solution sent out of the mixing and stirring apparatus 3 flows through the air bubble extinguishing apparatus 1.