To eliminate trouble such as the rise of turbidity or the generation of microorganisms by together using ozone treatment and activated carbon adsorbing treatment in a water purifying treatment apparatus wherein ozone treatment and activated carbon adsorbing treatment for removing a very small amt. of low molecular org. matter incapable of being removed by membrane separation treatment are combined with membrane separation treatment.

A water purifying treatment apparatus is equipped with a means 1 directly treating raw water with ozone, a fluridized bed type activated carbon adsorbing means 2 subjecting ozone treated water to activated carbon adsorbing treatment or a powder activated carbon adding means and a UF membrane separation means 3 subjecting activated carbon treated water to membrane separation treatment. By this constitution, a very small amt. of low molecular org. matter is efficiently removed by ozone treatment and activated carbon adsorbing treatment and activated carbon is removed by the membrane separation means. The permeability of a membrane is improved by the ozone treatment of raw water. Since the activated carbon adsorbing treatment means is provided between the ozone treatment means and the membrane separation means, the deterioration of the membrane by ozone can be also prevented.