A waste treatment system 100 for performing a hydrothermal treatment of wastes includes a hydrothermal treatment device 10 for performing the hydrothermal treatment by bringing steam into contact with the wastes, a storage facility 8, 9 for storing a fuel produced from a reactant of the hydrothermal treatment, and a heat recovery steam generator 18 for generating the steam to be supplied to the hydrothermal treatment device 10. The heat recovery steam generator 18 is configured to generate the steam by using a combustion energy generated by combustion of the fuel stored in the storage facility 8, 9.