Experiments were carried out on the flow visualization and velocity measurement of the wake behind a circular cylinder with a highly water-repellent wall with many fine grooves at the surface, in the Reynolds number range of Re=20^-150. By applying the boundary condition of fluid slip at the wall, the streamlines of flow past a circular cylinder were analyzed at Re=20 and 50 using the numerical calculation model. The analytical results were in good quantitative agreement with the experimental trace of the flow pattern, and the drag reduction phenomena of a circular cylinder were clarified from the calculated results of the pressure profile and the experimental result of the velocity profile of the wake. The drag reduction ratios of tap water, calculated using $ =4 pa- s/m for the sliding coefficient, are 15% and 10% at Re=20 and 50, respectively.