To enable a rolling reduction device for restraining horizontal movement by resistance force due to water cutting of a cylinder and weight of water itself gathered in the cylinder in the horizontal movement of becoming lateral swinging such as a pendulum, to not only reduce rolling while anchored but also quickly cope with a huge wave in sailing, by integrally fixing an upper side part of the cylinder to a ship, by vertically lowering a penetrated cylinder in the water while putting water in from an opening part of a lower end part of the cylinder when anchoring the ship.

Though sailing by pulling up the penetrated cylinder 1 on the ship from the inside of the water, a rope 7 of suspending the cylinder is pulled down once in a U shape to a deck 30 or the ship bottom 31 from a pole 6 together with a pulley 8, and in an emergency, the pulley is released by removing from the deck or the ship bottom by a pulley releasing mechanism arranged in the pulley, and the surplus length is generated at a stretch, and turnover is prevented by quickly lowering the cylinder of the rolling reducing device in the water even when meeting with the huge wave.