To provide an underwater eddy preventing apparatus for pump feed tank which avoids generation of vibration and noise by preventing generation of underwater eddies in both areas of a first protruding section in the cross direction, and miniaturizes of the pump feed water tank by increasing flow rate.

This pump feed water tank 3 is formed out of a closed cross-section structure surrounded by a bottom surface 4, both-side vertical surfaces 5, rear side vertical surface 6, and a ceiling 7 leading to a suction opening 2 of a drainage pump 1 and is structured so that the first protruding section 8 protruding to the front side in the center of the rear side vertical surface 6 in the cross direction may protrude uniformly from the bottom surface 4 to the ceiling 7. Between the bottom surface 4 of the rear side vertical surface 6 on both sides of the first protruding section 8 in the cross direction and the ceiling 7, second protruding sections 10, 10 of plate shape are protruded to the front side over the whole area of the first protruding section 8 in the cross direction and are provided horizontally.