In this paper, the author shows convenient formulas to calculate ship motions, shearing forces, bending moments in regular waves. From the results of theoretical calculations, it is found that the maximum bending moment occures at the forward position from the midship at high speed in long waves, affected by the pitching motion. But, the position is not so distant from the midship, and the value of the maximum bending moment is not so larger than that at the midship.