PROBLEM TO BE SOLVED: To provide a diffuser and a diffusion method by which fine bubbles are widely diffused and can be stably fed to a bottom layer.SOLUTION: The diffuser includes: plural rising water stream generation means 2 which are so located in water as to have a regular polygonal shape and respectively generate continuous rising water stream 15； and diffused material supply means 3 which discharges fine bubbles toward lowering water stream 18 of vertical circulation flow. The plural rising water stream generation means 2 generate a continuous diffusion flow 17, which is generated by the continuous rising water stream 15 and is diffused in a concentric circular shape, on respective upper water surfaces 10, induce continuous lowering water stream 18, which is directed to a water bottom 13 from the water surface 10 by mutual interference of adjacent diffusion flows 17, at a central part of the regular polygonal shape, thereby forming vertical circulation flow by the continuous rising water stream 15 and the continuous lowering water stream 18.SELECTED DRAWING: Figure 1【課題】底層へ微細気泡を広く拡散し、安定して供給することが可能な拡散装置および拡散方法の提供。【解決手段】水中に正多角形状に配置され、それぞれ連続的な上昇水流１５を発生させる複数の上昇水流発生手段２であり、それぞれの上方水面１０に連続的な上昇水流１５で生起される同心円状に拡散する連続的な拡散流１７を発生させ、隣り合う拡散流１７同士の相互干渉により正多角形状の中心部に水面１０から水底１３に向かう連続的な下降水流１８を誘起させて、連続的な上昇水流１５と連続的な下降水流１８とによる上下循環流を形成する複数の上昇水流発生手段２と、上下循環流の下降水流１８に向かって微細気泡を放出する被拡散物供給手段３とを含む。【選択図】図１
