The dynamical action of the movable weight contained in ships to the amplitudes of the oscillations is investigated by making use of the properties of the coupled oscillation of the double physical pendulum as a prototype of the simplified condition of the ship. The tightness of coupling of the oscillations is governed by J ₁, ratio of the moment of inertia of the secondary pendulum about the axis of oscillation with some reductions due to the length and the weight of the pendulum to the moment of inertia of the primary pendulum with fixed secondary pendulum, J ₂, ratio of the moment of inertia mentioned above to the moment of inertia of the secondary pendulum, and e ₁, ratio of the natural period of the primary pendulum with fixed secondary pendulum to that of the secondary pendulum. The results are summarized as follows : (1) The amplitudes of the primary pendulum at the higher frequency synchronism become in_ no case larger than that at the synchronism of pendulum with fixed secondary pendulum, and they are small in magnitude when e₁>1, so the higher frequency synchronism is less important. (2) The amplitudes at the lower frequency synchronism scarecely ever exceed that of the pendulum with fixed secondary pendulum and they are small, if e ₁<1, when J ₁ _??_0.050.1, but the range of el where the moving weight is effective as the oscillation absorber is restricted to smaller values. with increasing J ₁. The effect of J ₂ is rather complicate but is not serious as far as J ₁ is small. (3) Applying the above mentioned criteria to the cases of oil tankers with cargo oil. When the depth of the cargo oil is shallow, J ₂ is large but J ₁ and e ₁ are small, so the moving oil is effective as the oscillation absorber. When the oil is deep putting small values of J ₁ and J ₂ (negative) together large e ₁, it may be safely said that the oil is barely effective but is not harmful. (4) Giving the restriction to the amplitude of the secondary pendulum, the amplitude of the primary pendulum decreases remarkably by the collision damping.