In the railway ferry-boat for the Aomori-Hakodate route, especially the “Seikan-maru” No 5 and other ships of the wartime type which followed it, serious damage has been caused to the hull part near the fender which is liable to strike against the quay-wall. So that, the investigations are need for obtaining data for the theoretical designing of the ship structure near the fender by clarifying the impact force between the ship and quay-wall. In this paper, the author gives a result of theoretical study on the pressure between the ship and quay-wall in contact, according to the Hertz's theory of impact. In the hull part which is liable to strike against the quaywall, the equation of motion becomes as follows, where η+αηⁿ=0 η is displacement of this part. α equals to C/Me. c is constant, or the rigidity of the hull structure, Me is effective mass of ship. From the theory of contact, n equals to 1.35, then, solving this equation, he obtains the impact pressure between the ship and quay-wall as follows. F_max=1.097 C^0.4255•(M_eη0²)^0.5745