To provide a marine steam jet refrigerating/heat pump apparatus used for air conditioning for a cabin in summer as well as used for icing prevention on a gangway and a handrail in running of a vessel in winter.

An air stream produced by vaporizing a refrigerant in a steam generator 50 utilizing waste heat of a main machine and an auxiliary machine such as an engine 56 and a pump 53a in a vessel is guided to a nozzle of an ejector 52 as a driving air stream. The refrigerant from an evaporator 51 is mixed with the aid of suction effect of the ejector 52, and vaporized refrigerant injected from an outlet side of the ejector is guided to a conveyance passage. The conveyance passage is brought into thermal contact with a desired portion of the vessel or guided to a condensation space provided in a part of a vessel body for heat dissipation, and condensed heat is guided to the evaporator 51 and the steam generator 50 to construct a refrigerating or heat pump cycle.