To surely prevent a leaching out of a sewage to outside.

In a waste disposal plant, a recessing part 10 is formed by excavating the ground and a water shielding layer 12 is formed over the entire periphery at its inner surface. The water shielding layer 12 is composed of an upper and lower water shielding layers 12a and 12b having a double structure and a water permeable layer 12c lying between these layers 12a and 12b. Plural pipes 12d for water feeding and draining are provided at an inclined surface part of the water permeable layer 12c. The waste 14 is discarded in order on the upper water shielding layer 12a. The waste disposal plant having such a structure is controlled with a control device 16 so that a water level of the water permeable layer 12c may be higher than that of the waste 14.