In a design stage of large bridge over an important sea rout, many investigations such as observations and/or predictions of the sea traffic volume and researches on an effective support system for sailing have been considered. In the study on ship collision to piers, some considerations, namely a selection of target ship dimensions, the collision patterns, calculations of the collision energy and so on have been done. However, few researches have been carried out on the probability of drifting-ship collision to the pier on each parts of it. In practice, some large fenders as the shock absorbers have been installed on the four sides and corners around the pier, respectively. It is important and difficult to arrange the shock absorbers around the piers, safely and effectively. In this paper, a study on calculation method of probability of drifting-ship collision to a rectangular pier due to wind and tides were carried out considering positions of the pier. And a case study for a Japanese famous large bridge was demonstrated.