PURPOSE: To provide the titled apparatus excellent in sterilizing effect and capable of obtaining safe drinking water, constituted by arranging an ultraviolet lamp coated with a material having a water resistance and good perviousness in the main body of the apparatus provided on the way of a water distribution pipe for distributing water from an overhead water tank to each house.

CONSTITUTION: At least one or more of cylindrical apparatus main bodies 1 are provided on the way of a water distribution pipe for distributing pipe from the overhead water tank mounted to a middle or high building to each house in parallel or in series. A plurality of ultraviolet lamps 3 each coated with a material 2 having water resistance and good perviousness such as quartz are arranged in the above mentioned apparatus main body in the same axial direction and a detection apparatus 5 for detecting the lighting state of each ultraviolet lamp 3. In addition, one or plurality of stirring plates 4 having slits 4a are arranged in the apparatus main body 1 and flowing water is stirred to make it possible to enhance sterilization effect due to ultraviolet rays.