To provide a method and facility for desalination a carbonized product, wherein a smaller amount of washing water is used for desalination treatment of the carbonized product in carbonization facility of waste or sewage sludge, a closed system of washing water can be achieved and the carbonization facility and the desalination facility can be downsized.

The desalination facility 11 of the carbonized product produced in the carbonization facility of the waste or sewage sludge is provided. The desalination facility 11 is equipped with a mixing tank 12 for mixing the carbonized product with the washing water, a dehydrator 13 for dehydrating a mixture of the carbonized product and the washing water derived from the mixing tank 12 and a reverse osmosis membrane treatment apparatus 15 for filtering the dehydrated filtrate derived from the dehydrator 13 with a reverse osmosis membrane. A permeate from the reverse osmosis membrane treatment apparatus 15 is reused as the washing water in the mixing tank 12.