PURPOSE: To reduce the starting vibration of a propeller of a ship by providing a pair of planar members having a wing profile between the spherical stern portion and the stern extension directly above the spherical stern portion of the ship.

CONSTITUTION: Struts 6, 7 of wing profile are provided between the spherical stern portion 4a of a ship 4 and the stern extension 4b. Thus, water is concentrically gathered at this portion to reduce the wake to cause all the streams near the portion 4a to become the flow having only the velocity component of propeller axis toward the propeller 5 to thereby equalize the flow velocity of the stream entering into the propeller blades. Accordingly, since it can improve the flow velocity distribution of the stream entering into the propeller 5, it can reduce the starting vibration caused by the vibration of the hull and noise or the like.