PURPOSE: To form an artificial reef having good durability by a method in which many rock blocks are wrapped with a net of synthetic fibers integrally molded to form a bar-like material, and the outside of the bar-like material is bound at an adequate interval and at several points by ropes.

CONSTITUTION: Rock blocks 2 are housed in a long netted bag 1 made of a synthetic fiber, and the openings of the end portions of the bag 1 are strongly clamped with ropes. The outside of the bag 1 is strongly bound at an adequate interval at several points by ropes 3 to form an unit body (a). Plural unit bodies (a) are set on a basket 4, and the basket 4 is lifted up and laid on the seabed or river bed to form an artificial reef.