In order to control bubble removal or mixing in a flow channel, bubble transfer between flow channels (1, 2) is controlled by disposing first flow channel (1) for flow of a first fluid of liquid or gas and second flow channel (2) for flow of a second fluid of liquid with, interposed therebetween, gas exchange unit (5) through which while no liquid can pass, a gas component can be transferred, and by providing a pressure difference between the flow channels (1, 2) with the gas exchange unit (5). By rendering the pressure of the second flow channel (2) higher than that of the first flow channel (1), any bubble transfer from the first fluid to the second fluid is prevented, or bubbles within the second fluid are transferred into the first fluid to thereby attain deaeration.