It is important to understand an interaction between deformable surface and flow field surrounding it. In order to clarify this interaction, we had made some detailed experiments using several kinds of cylinder models having elasto-flexible surface in uniform water flow, and had found that on the surface were excited three different kinds of traveling waves, i. e. a continuously occurring wave, a periodically occurring wave and a randomly occurring wave. The present experiments were made to elucidate the mechanism of the wave generation and its propagation. The results showed that a relative frequency of the wave generation to that of the Karman vortex pair emission was linearly proportional to the power of 2/3 of the Reynolds number. This dependency is similar to the dependency of the wave propagation speed of Kelvin-Helmholtz instability in free shear layer on the Reynolds number. The traveling velocities of the waves were found to be about 65% of the main flow velocities regardless of the model diameter. Small vortices observed in the vicinity of the wave were found to move with same velocities as the wave propagating velocities. The velocity distribution in the shear layer of the separated flow around the cylinder was measured. The velocity at the inflexion point of the distribution was found to be same as the wave propagation velocity and the moving velocity of the small vortices. We concluded from the above results that the traveling waves were generated by the flow instability of the shear layer in the separated flow around the cylinder.