PURPOSE: To efficiently regenerate activated carbon using only sludge without containing mercury.

CONSTITUTION: Dehydrated activated sludge is fed into a drying kiln 4 to be heated and dried under stirring and the dried sludge is continuously sent into a carbonizing kiln 6 from the drying kiln 4 to be heated to the b.p. of mercury or higher in the carbonizing kiln 6 by high temp. gas and, after mercury is evaporated, the carbonized one is continuously discharged from the carbonizing kiln 6.