Treatment equipment for rainwater, etc. which can be easily assembled and constructed and has excellent mechanical strength. The treatment equipment for rainwater, etc. has a two-layer structure wherein a first layer and a second layer which are rectangular parallelepiped spaces are laid on top each other. A space of each layer is partitioned into 2*2 square spaces by six side plate members (3). In each layer, a pair of side plate members (3) are placed facing each other to be assembled into a square body, and the thus fabricated two square bodies are disposed adjacently to each other in an oblique direction. To make the layer spaces rectangular parallelepiped, the other two side plate members (3) are disposed in such a manner that end faces on both sides of each side plate member (3) may abut against the two adjacent square bodies. Two side end faces of one of the two square bodies face two side end faces of the other square body, forming a space between the two square bodies. A plurality of bar members (4) are inserted into the space surrounded by the two pairs of facing side end faces out of the plurality side end faces of the side plate members (3).