To provide a marine denitration system capable of supplying electric power to an ammonia producing device for producing ammonia for denitration while saving energy.

The marine denitration system comprises an ammonia producing device 2 to which electric power is supplied from an onboard power system 30, an SCR catalyst part 4 for carrying out exhaust gas denitration, a hybrid exhaust turbine supercharger for generating electric power using exhaust gas energy of a main engine 3 for supplying the electric power to the onboard power system 30, a shaft generator motor 13 that is capable of power-generation operation for supplying electric power to the onboard power system 30, and that is driven by the electric power supplied from the onboard power system 30 for energizing a propeller shaft 10, and a power management system 72 for controlling the supply of electric power to the ammonia producing device 2, the power generation output of the hybrid exhaust turbine supercharger, and the supply of electric power to and the power generation output from the shaft generator motor 13.