The water modification unit (1), which is provided with a treatment tank (200) for collecting and modifying raw water that is to be modified and a modification device body (100), which is for modifying water or an aqueous medium, is connected so as to allow circulation, kills microbes in the raw water, degrades components present in the raw water and coverts same to the reduced form, and also increases the surface activity of the raw water, is equipped with: a modification device with a radical-generating unit (101), a radical-amplifying unit (102), and a radical-eliminating unit (103) and a circulation means for circulating modification treatment of the raw water by circulating same between the treatment tank (200) and the modification device (100). The modification unit is provided with a control device for controlling the circulating modification treatment on the basis of the extent of reduction in potential using the oxidation-reduction of the raw water.
