It is known that flow structures similar to the famous Taylor vortex can be observed between an outer stationary cylinder and an inner rotating square cylinder, and one of their characteristic features is recognized to be the generation of waves at the boundary of each vortex cell and their propagation toward the outer cylinder wall. The main objective of this study is to investigate the generation process of the waves by using experimental and numerical visualization techniques. It was identified that, in addition to the characteristic vortex and wave structures, remarkable flow appears at the corner of the top (or equivalently the bottom) wall and the edge of the inner cylinder.