PROBLEM TO BE SOLVED: To efficiently dissolve a gas into a liquid in a wide range of the liquid by efficiently agitating_and_mixing the gas and the liquid and making the mixture of the gas and the liquid reachable a remote place in the liquid. SOLUTION: An apparatus for agitating-and-mixing gas and liquid has an agitation cylinder 20 haing an upper end part for introducing the gas and a lower end opened in the liquid, a rotary shaft 19 attached coaxially to the agitation cylinder 20, having an extended lower end and rotated at a high speed, an impeller 23 fixed to the lower end of the rotary shaft 19 and protrusively provided with an agitation blade piece 25 formed on the upper surface and a diffusion blade piece 26 formed on the lower surface of the shaft 19, and the impeller 23 is rotatably assembled in a clearance formed between the inside surface of the tube wall part of a main body part and the peripheral edge of the main body disk 24 to constitute a pump function part. The apparatus is constituted of the pump function part and a casing body K which is fixed to the lower end of the agitation cylinder 20, and a liquid introduction port is opened in the lower surface, and a release opening is opened in the cross direction. The mixture of the gas and the liquid is put on a liquid flow and released vigorously. COPYRIGHT: (C)2004,JPO