PROBLEM TO BE SOLVED: To obtain a structural material for building a seaweed bed capable of forming a seaweed bed having a high insertion ratio, also being producing easily and having a long lasting property. SOLUTION: This structural material is produced by arranging plural shaped frame plates 1, 2 coated with an algae-growing paint as a prescribed shape by putting the coated surface to the outside, joining these shaped frame plates 1, 2 with joining metal tools 3, also fixing the upper part of each of the shaped frame plates 1, 2 with an open stopping metal tool 4 and filling concrete to the inside of these shaped frame plates 1, 2 for making these shaped frame plates 1, 2 as one unit. A work of removing the shaped frame plates 1, 2 after placing the concrete is not required and also the paining work of the algae- growing paint at the working place of placing the concrete is not required.
