An apparatus for cleaning an object floating at the surface of water, e.g., a ship floating on the sea with ease and efficiency by use of a small amount of a cleaning agent is provided. This apparatus comprises a waterproof sheet having an area of covering a region to be cleaned of the object, and a buoyancy bag at its peripheral edge, air supply unit for supplying air into the buoyancy bag of the waterproof sheet laid under the object floating at the surface of water to float the waterproof sheet, so that a pool for accommodating the object is formed by the waterproof sheet, and a spacer for creating a clearance being filled with the cleaning agent between the waterproof sheet and the object accommodated in the pool. According to this apparatus, it is possible to clean the object floating at the surface of water on the spot without landing the object.