Provided is an anti-rolling tank. The anti-rolling tank comprises: a first ballast tank installed in a left side of a ship; a second ballast tank installed under the first ballast tank; a third ballast tank having the same height as the second ballast tank and installed in a right side of the ship; a fourth ballast tank installed on the third ballast tank; a first pipe connected between the first ballast tank and the third ballast tank; and a second pipe connected between the second ballast tank and the fourth ballast tank. When the ship is inclined toward the left, ballast in the first ballast tank moves to the third ballast tank due to its own load. On the other hand, when the ship is inclined to the right, ballast in the fourth ballast tank moves to the second ballast due to its own load. The anti-rolling tank effectively reduces sideway rolling of a ship in response to motion of the ship.
