PURPOSE: To efficiently perform washing of a filter by fitting a tubular nozzle freely to the inside of a cylindrical filter having ruggedness in the internal circumferential face and injecting steam through the nozzle hole.

CONSTITUTION: A nozzle 11 is made to a cylindrical shape having a closed tip and the long holes 12a, 12b wherein an oblique angle θ1 for an axial line O1 of the nozzle 11 is 45° are provided respectively while transferring the positions in the axial direction to the part opposite to the diameter direction of the external peripheral face in the tip thereof. General service steam of a ship fed to the nozzle 11 is injected through both the long holes 12a, 12b. The outside diameter R1 of this nozzle 11 is made to a size shorter by several millimeters than a cylindrical filter having ruggedness in the internal circumferential face such as a notched wire filter 5. Therefore the filter is rotated around the nozzle by steam injected through the nozzle hole of the nozzle 11 and washing of the filter can be performed.