The oscillation of a flexible tube in the vicinity of a copula with a rigid tube was studied experimentally in order to understand the basic behavior of the artery in the vicinity of a copula with a vascular graft. In this study, the emulsion was used as a substitute for blood because of its properties similar to blood. The radial displacement of the flexible tube and the flow rate of the emulsion were measured using a high sensitive gap sensor and an electromagnetic flowmeter respectively. The experimental results are summarized as follows : (1) The non-Newtonian property of fluid has the effect of increasing the amplitude of the flexible tube. (2) If a rigid tube is installed in the upstream side of a flexible tube, the amplitude of the flexible tube is increased markably. This effect becomes clear with the decrease in the stiffness of the flexible tube.