An apparatus for discharging condensate in an air cooler of a propelling engine for a ship while preventing the reverse flow of the condensate is provided to prevent destruction of an oil film between a cylinder liner and a piston ring due to the condensate. In a condensate discharging apparatus, the condensate generated in a water mist catcher(20) is firstly discharged to a leakage tank(40) and is secondly discharged to a venting tank(50) connected to the leakage tank by a leakage tank condensate discharge pipe(60) to separate and discharge the air in the condensate. The condensate generated in the air cooler is directly discharged to the venting tank through the air cooler condensate discharge pipe connected to the venting tank. The reverse flow of condensate is prevented by separating the condensate in the water mist catcher from the condensate in the air cooler.
