PURPOSE: To perform cleaning of outer plates of a hull by casters equipped with rotating brush running on the rails installed on fixing apparatuses and the bottom part of a building ship frame in such a way that a hull is housed through the fixing apparatuses on a U-letter shaped building slip frame in free command of going up and down in a dock.

CONSTITUTION: A building slip frame 1 is provided in the U-letter shape in free command of going up and down along stanchions 9 installed at the upper parts on both sides in a dock 6, a ship is housed on the building slip frame 1 by water infusing and draining operation into and from the dock 6. The ship is fixed through a retaining port 32, fixing apparatuses 15 on the building slip fame. Rails 31 are respectively installed on the fixing apparatuses 15 and on the bottom parts of the building slip frame, casters 4 equipped with rotating brush 5 run on the rails 31, to perform cleaning of outer plates of the hull.