To provide a rust preventive displaying sufficient rust-proofing effect to a metal part processed with a water soluble metal processing liquid and a metal wetted with the water, and even to a metal surface having projecting and recessed part.

Water-soluble organic solvent is used as the base and the rust preventive is added to the above solvent. This rust preventive displays the sufficient rust-proofing effect to the metal surface being wetted with the water and even having projecting and recessed part, and displays the performance for sufficiently dissolving the water-soluble processing liquid attached to the metal.