In this study, a compressible low-Reynolds number flow over a circular cylinder was investigated by schlieren visualization and the force measurement. A Reynolds number based on freestream quantities and a diameter of a cylinder is set to be 1000 ≤ Re ≤ 5000 and a Mach number is set to be 0.1 ≤ M ≤ 0.5 by using the low-pressure wind tunnel. From the schlieren visualization, frequency of the vortex shedding was obtained by performing frequency analysis on the time series schlieren images. Near wake structure by the circular cylinder is measured by time-averaged schlieren image. Even though M is less than 0.5, the structure of the flow fields changes depending on M. The effect of M on the scale of wake structure depends on Re. Under the condition at Re of 1000–3000, the scale becomes large as M increases more than 0.2. On the other hand, under the condition that Re is 4000–5000, it becomes small as M increase 0.3 or more St is revealed to be decrease for Re of 2000–3000 with increasing M, and St increases at Re of 4000–5000. From the force measurement, drag coefficient (Cd) and pressure distribution on a circular cylinder (Cp) obtained. The effect of M on Cd does not depend on Re, and Cd also increases as M increases. The effect of Re on Cd is also observed that Cd increases as Re increases and this trend doesn’t depend on M. The Cp decrease with Re increase. The M effect on Cp is that the range of Cp is enlarged with M increase.

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