PROBLEM TO BE SOLVED: To reduce a site space required for an artificial wetland.SOLUTION: An artificial wetland for water quality improvement 10 using decomposition of organic substances and nutrient salts by microbes comprises: an accumulated filter bed unit 20 in which filter beds 22, 24, 26 and 28 forming biofilm or plant rhizosphere microbial communities are piled up in plural layers in a vertical direction in which water falls by gravitation; pipe lines between filter beds 40 provided between the filter beds 22, 24, 26 and 28 in the accumulated filter bed unit 20; and drainage pipe lines 60 arranged in a bottom side of the bottom filter bed 28 in the accumulated filter bed unit 20 and draining away the water from the bottom of the bottom filter bed 28. The pipe lines between filter beds 40 are formed with multiple air supply lines 42, 44 and 46.
