To provide a method for manufacturing a cement cured body for easily building a large-sized structure which creates best-suited environments for the proliferation of the underwater life and is of a high strength.

The base and side of a form 2 are internally lined with a porous cement cured body 1 of a specified shape. Next, a ready mixed concrete is deposited in the form 2 and is cured to a specified strength to form a concrete part 3. After that, the form 2 is released to obtain a composite cement cured body 4 which is composed of the porous cement cured body 1 having a continuous void formed internally and the concrete part 3, joined together. The part near the surface of the composite cement cured body 4 is formed of the porous cement cured body 1, so that the best-suited environments for the proliferation of the underwater life can be created. In addition, as most of the composite cement cured body 4 is formed of concrete, it is possible to build a large-sized structure of a high strength.