PURPOSE: To produce a rust preventive improved in the corrosion resistance of a rust preventive coated film by preparing the rust preventive composed of a boric acid based compound and a polyol and having a skeleton expressed by a specific formula to improve the film forming property of a coating material.

CONSTITUTION: The rust preventive having the skeleton expressed by the formula is made of at least one of the boric acid compounds selected from a group composed of boric acid (H3BO3), the polycondensed acid of boric acid (HBO2, H2B4O7), ammonium borate and/or ammonium salt of polycondensed acid of boric acid ((NH4)2B4O7, NH4B5O8, (NH4)2B8O12 or the like) and at least one of a complex compound selected from a group composed of the polyol (ethyleneglycol or the like), polycarboxylic acid (terephthalic acid or the like) and a compound (glycol or the like) having OH group and COOH group in a molecule. By using a rust preventive coating material containing the rust preventive, the corrosion resistance of a steel sheet is improved.