To provide a marine denitration system capable of stably supplying electric energy needed for producing ammonia as a reducing agent for denitration.

The marine denitration system 1 comprises: an ammonia producing device 2 having a hydrogen producing part 81 for producing hydrogen from water, and a nitrogen producing part 83 for producing nitrogen from air, and for producing ammonia from the hydrogen produced by the hydrogen producing part 81 and the nitrogen produced by the nitrogen producing part 83; and an SCR catalyst part 4 provided in a second exhaust pipe L2 as an exhaust gas passage of a marine propulsion diesel engine 3 for carrying out exhaust gas denitration with the ammonia produced by the ammonia producing device 2. A hybrid exhaust turbine supercharger 5 and a storage battery 67 are provided for supplying the power generation output of the hybrid exhaust turbine supercharger 5 and the storage battery to the ammonia producing device 2.