To provide a method capable of treating waste originated from mollusk inexpensively, highly safely and with a high added-value and capable of treating heavy metals.

The waste originated from the mollusk is decomposed by at least one side of super critical water or subcritical water. According to the method, the waste is decomposed into substances of high value-added such as organic acid, phosphoric acid, amino acid and fatty acid. Moreover, when the waste contains heavy metals, the heavy metals can be concentrated to a specified division. One example thereof is shown in Fig. As shown in Fig., according to the method for treating waste, great part of cadmium included in digestive tract, for example, can be concentrated to a fat phase and a solid phase. Therefore, according to the method for treating waste, the waste originated from mollusk containing heavy metal, for example, can be effectively turned to resources. In the method for treating waste, the subcritical water is preferably used in respect of decomposition ability, safety, equipment cost and running cost etc.