The flow patterns around a circular cylinder placed on a flat plate are visualized by an oil-flow method and a china-cray method in high-subsonic flows; Mach numbers are 0.3, 0.4, 0.5 and 0.6. As well as the flow visualization, pressure distribution on the flat plate is measured. As the results of the flow visualization, it is clarified that a horseshoe vortex around the circular cylinder, which has already been observed in lowspeed flows and supersonic flows, is also observed in high-subsonic flows. The results of the pressure measurement indicate that the influence of the circular cylinder height on the flow field is greater than the influence of the Reynolds numbers.