To provide a water treatment apparatus allowing sufficient washing of the surfaces of glass tubes contacting with treated water.

This water treatment apparatus includes: a treatment water tank 1 through which the treated water can flow; lamp devices 2 disposed inside the treatment water tank 1, and including protective tubes 22 as the cylindrical glass tubes; and a washer 7 including washing bodies 735 capable of washing the surfaces of the protective tubes 22 contacting with the treated water. By moving the washer 7 along the protective tubes 22, the outer surfaces in a tube axis direction of the protective tubes 22 can be washed by the washing bodies 735. By rotating the washing bodies 735 by the water flow of the treated water, the outer circumferential faces of the protective tubes 22 can be washed by the washing bodies 735.