PROBLEM TO BE SOLVED: To provide a soluble collagen compact constituted of collagen fibers, and having a porous spongy shape capable of three-dimensional cell cultivation.SOLUTION: A soluble collagen fiber porous body is obtained by freeze-drying fibrotic collagen deposited by an alkali metal bicarbonate. A soluble collagen compact produced by the method has a porous spongy shape capable of three-dimensional cell cultivation, while keeping a fibrous structure by the collagen.