A water treatment unit (10) performs a normal operation during which discharge parts (31-34) generate an electric discharge in a state where water flows into a treatment vessel (11) and treated water flows out of the treatment vessel (11). When the water treatment unit (10) starts operating, the water treatment unit (10) performs a preparatory operation for a predetermined period of time before starting the normal operation. During the preparatory operation, the discharge parts (31-34) generate an electric discharge in a state where an outflow of the water from the treatment vessel (11) is stopped. As a result, the water which has been stagnating in the treatment vessel while the water treatment unit is not operating and in which bacteria have grown is sufficiently sterilized.
