To obtain a resin composition forming a corrosion resistant coating having excellent acid-resistance and alkali-resistance by adding a phenol/ formaldehyde copolymer and a polyimide resin with a glycidyl epoxy resin.

100 pts.wt. of the first resin composition forming a corrosion resistant coating is obtained by blending 60-80 pts.wt., preferably 65-75 pts.wt., of a glycidyl ether epoxy resin having a viscosity (25°C) of 100-5,000 cPs and an epoxy equivalent of 150-450, 2-15 pts.wt., preferably 2-10 pts.wt., of a phenol/ formaldehyde copolymer and 18-30 pts.wt., preferably 20-30 pts.wt., of a melamine/formaldehyde resin. 100 pts.wt. of this first resin composition forming a rust-resisting-coating is blended with 5-20 pts.wt. preferably 7-16 pts.wt., of the second resin composition forming a corrosion resistant comprising 60-80 pts.wt., preferably 68-75 pts.wt., of a glycidyl ether epoxy resin and 20-40 pts.wt., preferably 23-38 pts.wt., of a polyimide resin.