PROBLEM TO BE SOLVED: To create an environment, in a sea, a beach, a river or a vicinity of a river bank, that retains objects for generating iron humate or humic acid effective for cultivating algae and is suited to proliferation of organisms.SOLUTION: An organism cultivation block includes: a block body 1 formed from a porous cement hardened body having a continuous void therein； a storage part 2 that is a space formed inside the block body 1 and communicated to an external surface of the block body 1； and an organism cultivation additive material 4 to be stored in the storage part 2. The organism cultivation additive material 4 used may be an object formed by enclosing a material that is formed by blending humic soil and iron, in a bag body formed of a water-permeable material. The external surface of the block body 1 may be provided with inhabitation holes 3. Preferably, the bore diameter of the inhabitation hole 3 is formed gradually smaller, as it heads toward the depth direction, and communication holes 5 opened to the external surface of the block body may be connected thereto.
