Abstract: Improvements are made in the known apparatus for collecting effluent oil of the type such that the apparatus includes a pair of left and right side plates disposed at a predetermined distance in a forwardly opened arrangement, a weir plate mounted to said side plates as inclined in a rear-downward direction so that its opposite side edges may contact with the inner wall surfaces of said respective side plates under a water surface, a slant plate disposed with its rear end positioned above the rear end of said weir plate at the rear ends of said side plates and having its opposite side edges fixedly secured to the inner wall surfaces of said side plates, an oil leakage preventing plate positioned in the midway between the rear end of said weir plate and the rear end of said slant plate and having its opposite side edges fixedly secured to the inner wall surfaces of said side plates to form a water discharge port between said oil leakage preventing plate and the rear end of said weir plate and to form an oily w