A supersonic parachute is one of effective and promising deceleration processes at entry into a planet. However, fundamental researches on its aerodynamics, particularly at its opening phase, have not been fully carried out. In this study, flow fields in/around simple configurations that modeled a supersonic parachute at its opening are discussed using computed fluid dynamics. Results indicate that pressure inside the parachute is exposed to twice (at the maximum) as large as the pitot pressure at Mach 2. In addition, the so-called "breathing," which is a more characteristic unsteady phenomenon, appears due to the internal pressure fluctuation, which changes the position of the detached shock wave periodically. Finally, at a higher Reynolds number, the boundary-layer inside the parachute became thinner, leading to more complex shock/boundary-layer interactions.