To make a catch basin a downward gradualy thin inclined face by forming a notch part on the side wall of a charnel house, fitting the catch basin, forming the upper part of the catch basin thick, and forming the lower part thin.

The notch part 7 is provided on the side wall of a charnel house M to fit the catch basin N to the notch part 7. At the same time, the upper part of the catch basin N is formed thick, the lower part is formed thin, and the outside face of the catch basin N is made the downward gradually thin inclined face. In other words, the notch part 7 is drilled on the center upper part of the right and left side walls 2, 3 of the charnel house M. The catch basin N formed in the same shape therewith is fitted on the notch part 7. Furthermore, the prescribed number of ventilation small holes 8 are horizontally and vertically drilled in the catch basin N in the horizontal and vertical directions at regular intervals. The ventilation of the inside and outside of the charnel house M through the ventilation hole 8 is enabled, and inside humidity is removed as soon as possible. Thereby the leakage of rainwater from the outside can be prevented as soon as possible.