<；P>；PROBLEM TO BE SOLVED: To provide a biofilter apparatus which can periodically change the water level in a treatment tank without being equipped with a controller and can efficiently purify water to be treated while maintaining the flowability of a floating biofilm carrier. <；P>；SOLUTION: The biofilter apparatus includes a filter tank 2, number of floating biofilm carriers 5 which are filled in the filter tank 2, can move through water, and are formed with a microorganism film on their surfaces, a water tank 8 which has a water surface at a position lower than the height of a water distribution port 2c defining the lower limit of the water level in the filter tank 2, a siphon tube 7 whose one end is connected to the water distribution port 2c of the filter tank 2, whose other end is immersed in water of the water tank 8 for receiving the supply of filtered water from the filter tank 2, and whose middle portion 7c is located at the height of the upper end of the filter tank 2 or at the height of a position closer to the upper end of the filter tank 2, and a water supply portion for supplying the water in the water tank 8 from above the filter tank 2. <；P>；COPYRIGHT: (C)2010,JPO&INPIT
