To wash out salts deposited on a bridge and prevent rust by attaching pipes at both inside and outside faces of the constituting members of the bridge and supplying water in a water storage tank to the pipes to eject it from nozzles arranged at the front ends of the pipes.

Rainwater or snow or the like on the floor face of a bridge 1 is collected in a water storage tank 2 through water pipes and washing water is added thereto when necessary to wash out salts deposited on the constituting members of the bridge 1 by the water in the storage tank 2 through pipes 4. A plurality of nozzles 5 are installed in the pipes 4 to eject water to the constituting members of the bridge. Salts, dust, or the like with which girders or the rear face of the slab of the bridge 1 is stained, is removed and cleaned with cleaning water containing a cleanser. Thereafter, the cleaning water is washed out with fresh water and a coating agent is sprayed thereon. In this way, salts, dust or the like chiefly causing rust generated on the constituents of the bridge 1 can be removed to prevent rust.