PURPOSE: To provide a swing suppressing device which prevents the collision of a swing suppressing plate with a quay or other vessels and generates a large swing suppressing effect by suppressing the projection of the outer edge of the swing suppressing plate outside a gunnel, in use, and permitting the use of the outer edge in a deep water part where the wave motion radius is extremely small.

CONSTITUTION: The basic edge part of a swing suppressing plate 4 which is constituted so that a plate surface 7 is set almost perpendicular to the swing direction is axially supported at an axial supporting part which projects rearward from the transom 2 of a hull 1, and the swing suppressing plate 4 is turned downward from an accommodation state, and is used in the state projecting downward from the ship bottom slantly downward outwardly.