The motion is investigated of a box-type floating vessel which is moored among the regular waves in the sea of finite depth by the chains and on which the constant drifting force acts. The present authors assume the floating vessel to be very blunt, and the length-breadth ratio of investigated one is 1. The aim of the present report is to investigate the following problems : (1) Is the strip method acceptable for such a blunt body as the above mentioned from the engineering standpoint ? (2) How much is the nonlinear effect of the chain reaction on the motion of the floating vessel ? The linearized equations of motion are solved analitically. On the other hand, the nonlinear equations of motion are integrated numerically by Runge-Kutta-Gill method. The results of the theoretical calculations show the followings : (1) If the various damping forces of the rolling motion could be estimated in any way, the motion of the blunt body among the waves may be estimated by the strip method. (2) If the initial tensions of the chains are small, the nonlinear effect of the chain reaction on the stationary harmonic motion of the floating vessel is very small. A rough standard condition for the small tension is that the chains touch horizontally the sea bottom at the anchoring points. (3) When the unstationary or constant drifting force acts on the moored floating vessel and it drifts from the initial equilibrium position largely, the nonlinear effect of the chain reaction is very large. Hence, the motion in the irregular wave, under the constant drifting force or under the large initial tension should be estimated considering the nonlinearity of the chain reaction.