PURPOSE: To improve the strength and to manufacture easily by forming a main catchment and drain by fixing the circular plates in such a state providing a slit-like gap between their mutual end edges by means of the internal and external double round tube.

CONSTITUTION: The plural number of circular plate 2 is inserted and held between an annular fixture 5 without the tube and an annular fixture 4 within the tube provided to the inside of the plate 2 in such a state providing a slit-like gap between their mutual end edges. The plates are integrally fixed by fitting of a recessed section 7 for fitting provided to the outer surface of the annular fixture 4 within the tube with a projected section provided to the inner surface of the annular fixture 5 without the tube so as to correspond to the recessed section to form a main catchment and drain 1. According to the constitution, the slit provided between plates 2 for draining the underground can be widely obtained, but, at the same time, it can be easily manufactured as well as its strength improved.