PURPOSE: To make simultaneous removal of org. matter as well together with various ions by passing water in a refining stage to a mixed bed composed of ion exchange resins and active carbon in a process for refining primary pure water to ultrapure water.

CONSTITUTION: The water in the refining stage is passed to a mixed column 11 of the ion exchange resins and active carbon in the process for refining the primary pure water to the ultrapure water. More specifically, the ion exchange resins capture the various ions in the ultrapure water and the inorg. matter eluted from the active carbon, and the active carbon captures the org. matter eluted from the ion exchange resins and other org. materials, in the mixed bed composed of the ion exchange resins and active carbon in the mixed column 11 and, therefore, the effects which the ion exchange resins and the active carbon possess complement each other and the inorg. matter and org. matter can be simultaneously removed. The ion exchange resins in the ultrapure water have an adsorption effect and sterilization effect on bacteria, and is effective in preventing the propagation of bacteria in the mixed bed.