PROBLEM TO BE SOLVED: To provide a method and a device for producing pure water capable of preventing the generation of the occlusion of the electric demineralizing device and the deterioration of water quality of the treating water and capable of preventing the reduction of the treating efficiency of the electric demineralizing device and capable of preventing the shortening of the life of the device.SOLUTION: In the method for producing pure water alternately repeating a pure water producing treatment demineralizing by the electric demineralizing device 14, and a hot water sterilization treatment sterilizing by feeding hot water to the electric demineralizing device 14, the flowing direction of the water to be treated in the condensing chamber 142 of the electric demineralizing device 14 is set to be a countercurrent direction to the flowing direction of the water to be treated in the demineralizing chamber 141 during the pure water producing treatment, and the flowing direction of the water to be treated in the condensing chamber 142 of the electric deionizing device 14 is set to be a concurrent flow direction to the flowing direction of the water to be treated in the demineralizing chamber 141 during the hot water sterilizing treatment.
