PURPOSE: To prevent the corrosion of the titled apparatus due to impurities, in a method wherein the moisture in an exhaust gas is recovered to be supplied to an engine along with fuel, by using a water separating membrane selectively permeating steam in the recovery of moisture.

CONSTITUTION: A water separating element 13 has a water separating membrane 21 impregnated or coated with hydrophilic substance such as lithium bromide, polyvinyl alcohol or the like. An air circulation chamber 22 and a separated moisture chamber 23 are formed by this membrane 21 and the separated moisture chamber 23 is connected to the suction port of a pump 15 through an outlet 25. The water separating element 13 is interposed in the suction passage 11 provided to the downstream side of the air cleaner of an engine and moisture separated in the element is sent to a tank 17 under pressure through an arranged pipe 18 by the pump 15. At the time of use, the moisture is emitted from an arranged pipe 18 connected to the tank 17 through a valve 19. Because clean water free from impurities such as nitric acid, sulfuric acid or the like is collected by this apparatus, the corrosion of the apparatus is not generated.