To provide a water level electrode of a filter, which makes it difficult for activated carbon particles to adhere on an outer surface of an insulating surface of the water level electrode and can always detect the normal water level.

The water level electrode to be attached to a filter wall of an activated carbon filter S by screwing is configured in such a manner that a filter inner portion 22 protruding at least toward the filter inside of an insulator 1 is formed into a round bar, and the outer peripheral surface thereof is coated with a good water-repellent material.