To use gathered shells in sweeping of a seawater intake channel of a power generating station as an auxiliary material of a greening base material for preventing a face of slope from being eroded, by a simple treating facility.

Shell sludge taken out of the seawater intake channel is dried as it is to about 10% water content by a rotary drier 10 while crushing a part of shells to obtain dried shells 13. The dried shells 13 are treated as they are by an air classifying crusher 17 to obtain crushed shells. The crushed shells are intermittently bagged 22 as they are and, further, are shipped to a specialized greening base material manufacturing plant. Since transportation of the dried shells from the drier 10 to the air classifying crusher 17 is executed by negative pressure air stream at that time, the facility is simplified by using whirling stream of a gas cyclone in common.