To provide a water treating device and a water treating method for treating polymeric organic matter-containing water capable of inhibiting fouling of a membrane to stably operate the device.SOLUTION: A water treating device 1 for treating polymeric organic matter-containing water containing a polymeric organic matter, includes: a water tank 10 for storing polymeric organic matter-containing water； a raw water tank 12 for storing the polymeric organic matter-containing water from the water tank 10； an ozone treating device 22 as peroxide-adding means for adding peroxide while circulating the water stored in the raw water tank 12； a membrane filtration device 14 for subjecting the water stored in the raw water tank 12 to membrane filtration treatment； concentrated water returning means for returning at least a part of concentrated water obtained by the membrane filtration treatment to the raw water tank 12； an activated carbon treatment device 18 as peroxide decomposition means for subjecting the peroxide contained in the membrane filtration water obtained by the membrane filtration treatment to decomposition treatment； and treated water returning means for returning at least a part of treated water subjected to the decomposition treatment by the activated carbon treatment device 18 to the water tank 10.SELECTED DRAWING: Figure 1【課題】膜のファウリングを抑制し、安定した運転が可能な、高分子有機物含有水を処理する水処理装置および水処理方法を提供する。【解決手段】高分子有機物を含む高分子有機物含有水を処理する水処理装置１であって、高分子有機物含有水を貯留する水槽１０と、水槽１０からの高分子有機物含有水を貯留する原水槽１２と、原水槽１２の水を循環しながら過酸化物を添加する過酸化物添加手段であるオゾン処理装置２２と、原水槽１２の水を膜ろ過処理する膜ろ過装置１４と、膜ろ過処理で得られる濃縮水の少なくとも一部を原水槽１２に返送する濃縮水返送手段と、膜ろ過処理で得られる膜ろ過水の過酸化物を分解処理する過酸化物分解手段である活性炭処理装置１８と、活性炭処理装置１８により分解処理した処理水の少なくとも一部を水槽１０に返送する処理水返送手段と、を備える水処理装置１である。【選択図】図１
