PURPOSE: To eliminate the troublesomeness of the replacement of a battery and to reduce the maintenance cost accompanying the replacement of a filter to a large extent.

CONSTITUTION: The water purifier 1 consists of a battery unit D and a filter unit F connected to each other in a detachable manner. The battery unit D is equipped with a solar cell 2 generating low voltage 2, a storage battery 3 storing electric energy generated in the solar cell 2, an anode 4 and a cathode 5 and is integrally received in a battery case 6. The filter unit F consists of a conductive filter 10, the cylindrical filter case 9 housing the filter 10 and a lower case 11 having a water inflow port 11a and a formed thereto. By applying a low voltage to the conductive filter 10 from the storage battery 3 storing energy of the solar cell 2 through the anode 4 and the cathode 5, the propagation of bacteria in the filter 10 is suppressed.