To execute a pretreatment of coating of a casting with a short treatment time without generating chips, waste liquids, etc., and without using consumables, such as grinding wheels, abrasive powder and etchants, at the time of the treatment by bringing a member into pressurized contact with a casting surface, thereby plastically deforming the surface and making the ruggedness on the casting surface smaller.

The casting surface 22 of an aluminum cylinder is a surface under the working treatment. Projecting parts are annihilated on the casting surface 23 in the upper part of the aluminum cylinder by the pressurized contact and plastic deformation by a roller 16. Recessed parts begin to be annihilated by the build-up of the surface by the plastic deformation in the central part as well. The treatment of the recessed parts can be executed simultaneously with the compression of the projecting parts in such a manner and, therefore, the processing treatment time is short. In addition, the plastic deformation by the compression is merely applied on the casting surface 23 and, therefore, the dimensional accuracy prior to the processing treatment is not impaired and the generation of the chips, etc., is averted. Further, the casting blowholes existing at the surface layer and within the inside before coating are made extremely little and be annihilated by pressurized contact.