The solution method to the problem of a floating elastic disk subject to a train of plane waves is presented. This method is based on Stoker (1957) 's work and Ohkusu & Namba (1998) 's method using the assumptions of linear long wave theory, shallow draft approximation and Bernoulli-Euler equations for a thin plate. Solving an extended differential equation of Bessel in the disk domain, its velocity potential is matched to the exterior solution in the water domain. Some numerical results using this semi-analytical method are shown for a rigid or flexible disk relative to the length.