The contact wire corrugation occurred in Shinkansen Lines adversely affects the performance of current collection. It is important, therefore, to clarify its generating mechanism and establish effective countermeasures against this phenomenon. The author proposes a simple model in which a contact wire is represented as an infinite tensioned beam and a pantograph as several point masses. The growing rate of corrugation amplitude is calculated as a function of train velocity and wave length by using the contact forces generated by given sinusoidal irregularities. The model shows high growing rates in some velocity-wave length regions which essentially agree with conditions to generate real line corrugation. It is considered that in a contact wire excited at two points the deformation wave is represented as a sum of those from the two points and under some conditions the wave is completely canceled in the outside of exciting points. As the intrinsic mechanism, it is considered that the contact force and the irregularities become in phase with each other due to interference between the waves.