PROBLEM TO BE SOLVED: To provide a marine structure capable of easily creating an environment suitable for survival of marine life around a metallic structure placed in the sea.SOLUTION: The marine structure 1 comprises leg parts 2 placed in the sea W and acting as cathodes, and an anodic material 4 electrically connected to the leg part 2 and acting as an anode in the sea W. The leg part 2 is made of steel and the anodic material 4 is made of e.g., a magnesium-based material. In this way, calcareous matter is deposited as an electrodeposited mineral layer on the surface of the leg parts 2 in the sea W.