Wave excitation has been calculated by Grim based on the diffraction potential for two dimensional bodies of Lewis form sections. On the other hand, it has been suggested by Newman making use of Haskind relation that wave excitation could be induced from the radiation potential for which many works have been done by Ursell, Tasai and Porter on two dimensional bodies of Lewis form sections. In this paper, the author deals with the wave excitation due to beam seas on two dimensional ships of arbitrary sections making use of singularity distributions on the ship surface. The radiation potential induced by such singularity distribution was calculated, and the wave excitations for heave resolved into in-phase and out-of-phase components were obtained making use of the Kochin function. The author also extended the same technique into calculation of wave excitation in oblique waves including head seas. The calculation on wave-excitationless ship forms was performed, which showed satisfactory agreement with model experimental results. The calculation on three dimensional wave-excitationless ship forms was also done by means of the Strip Method. The results were in good coincidence with model experiment data.