It is an object of the present invention to provide a water purification apparatus and a method thereof utilizing an elongated closed water channel, and having increased purification efficiency and facilitated maintenance. The filtration apparatus 1A is provided with: a plurality of tube bodies arranged in parallel with their longitudinal directions directed in the vertical directions； and communication parts adapted to connect adjacent pairs of the tube bodies, thereby forming a water channel. The communication parts connect the tube bodies arranged in parallel alternately on upper and lower sides of the tube bodies. The tube bodies constitute the biofiltration part by aerobic bacteria, and the tube body constitutes the biofiltration part by anaerobic bacteria. The communication part is equipped with a control valve adapted to arbitrarily control a flow rate of water to be purified flowing into the tube body.
