To effectively inhibit the rolling of a ship without increasing the resistance in ordinary navigation to prevent an accident such as a capsize.

In this small-sized ship having the displacement tonnage of approximately 20 ton or less, rolling control members 3 are mounted on side outer boards 1a arbitrarily switchably between a laterally outwardly projecting state and a non-projecting state, and the rolling control members 3 are sunk into the water surrounding the hull 1, when the rolling control members 3 are laterally outwardly projected, and the hull 1 is rolled at an angle more than a predetermined angle, to produce the rolling control force with the interaction with the water.