An elongate rectangular cultivation box having an open top, is configured so as to allow an outer tank, which serves as a cultivating water storage part, and an inner tank, which serves as a receptacle for bivalves (benthic organisms) S that are to be cultivated, to be both combined and separated. A gap that serves as a water supply opening and a gap that serves as a space in which sediments can accumulate on the bottom of the outer tank are defined when the inner tank is accommodated in the outer tank. Water passage holes are provided in the bottom of the shellfish receptacle (inner tank) and a mesh filter such as netting is stretched across the top face of the bottom. The cultivation boxes are arranged in a vertically stacked manner, with the front portions and rear portions thereof staggered so that cultivation water W that overflows over a front ledge of a shellfish receptacle flows downward into the supply water storage part of a lower cultivation box.
