To provide a determination device capable of determining possibility of lowering of opening pressure in a fuel valve with a simple constitution, and a ship-ground communication system provided with the same and a determination method.SOLUTION: There are provided an in-cylinder pressure detector, an exhaust gas temperature detector, a determination unit, and a state value calculator. The state value calculator acquires a first state value indicating a deviation from a first reference value in a compression pressure and/or a second state value indicating at least one of a progress degree of occurrence timing of combustion start time pressure from a second reference value and an increase degree of a pressure difference obtained by subtracting the combustion start time pressure from the combustion pressure from a third reference value. When a combustion pressure decreases below a combustion pressure reference value and the exhaust gas temperature decreases below an exhaust gas temperature reference value, the determination unit determines the possibility of fuel leakage lower as the first state value is larger and/or determines the possibility of fuel leakage higher as the second state value is larger.SELECTED DRAWING: Figure 2