In old times, P. Watts was struck with an idea of reducing the rolling by water-chambers when he examined the report on the “Inflexible” by W. Froude. Since then this problem has been studied by several investigators. One of the authors has been studying on the shallow water waves in an oscillating tank. In this paper authors aim to study the action of the moment produced by shallow water waves in a rectangular tank as an apparatus to reduce the rolling motion. At first the moments were measured by means of the bench test, and they were compared with calculated values. Both results were in good agreement. Then a ship model having these tanks was examined in several conditions how they were effective as the anti-rolling device. Obvious effects were observed in the experiments on irregular waves as well as on regular waves.