Provided are a water treatment device and a water treatment method for treating polymeric-organic-matter-containing water, the device and method being capable of suppressing fouling of a membrane and being capable of operating in a stable manner. A water treatment device 1 for treating polymeric-organic-matter-containing water that contains polymeric organic matter, wherein the water treatment device 1 comprises: a water tank 10 for retaining the polymeric-organic-matter-containing water； a raw water tank 12 for retaining the polymeric-organic-matter-containing water from the water tank 10； an ozone treatment device 22, which is a peroxide-adding means for adding peroxide while circulating water in the raw water tank 12； a membrane filtration device 14 for performing a membrane filtration treatment on the water in the raw water tank 12； a concentrated-water-returning means for returning at least some of concentrated water obtained in the membrane filtration treatment to the raw water tank 12； an activated carbon treatment device 18, which is a peroxide-decomposing means for performing a decomposition treatment on peroxide in membrane-filtered water obtained in the membrane filtration treatment； and a treated-water-returning means for returning at least some of treated water that was subjected to the decomposition treatment by the activated carbon treatment device 18 to the water tank 10.L'invention concerne un dispositif et un procédé de traitement d'eau contenant des matières organiques polymères, le dispositif et le procédé étant capables de supprimer l'encrassement d'une membrane et pouvant fonctionner de manière stable. L'invention concerne un dispositif de traitement d'eau 1 contenant des matières organiques polymères, le dispositif de traitement d'eau 1 comprenant: un réservoir d'eau 10 servant à retenir l'eau contenant des matières organiques polymères ； un réservoir d'eau brute 12 pour retenir l'eau contenant des matières organiques polymères à partir du rés
