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 2 is installed at an axial supporting part which projects slantly in the vicinity of the underline on the rear surface of the transom 11 of a vessel so that the plate surface is set almost parallel to the transom 11 surface, and when the swing suppressing plate is turned downward, the plate surface is set nearly perpendicular to the swing direction, and projects downward to the ship bottom, and the top edge is set inside for the outermost side of the vessel.