PURPOSE:To simplify and ensure coupling of the flanges of a corrosionproof cover, by a method wherein a male type member and a female member, being located to the inner surface of the flange of the corrosion proof cover, are resiliently intercoupled, and a pin is extended through the male type and the female type member. CONSTITUTION:In the coupling mechanism of a corrosionproof cover 10, consisting of a pair of cover half bodies 10a and 10b with which the tide area and the splash area of a steel pipe 12 are covered, a male type member 20 is secured to the inner surface of a flange 18a of the one half body 10a, and a female member 22 to the inner surface of a flange 18b of the other cover half body 10b. The male type member 20 is resiliently engaged with the female type member 22 by means of gears 24 and 26, respectively, and a pin 35 is extended through the male type member 20 and the female type member 22. A gap between the steel pipe 12 and the corrosionproof cover 10 is filled with a filler for curing. This simplifies and ensures intercoupling of the flanges 18a and 18b of the corrosionproof cover 10 with the aid of the male type member 20, the female type member 22, and the pin 35.