Two-dimensional stress waves in an elastic circular tube are analyzed numerically when axisymmetric impacts are applied to the end face of the tubes. For the numerical analysis, a finite difference method along the bicharacteristic is bicharacteristic is employed. By obtaining the numerical results for various tube sizes, and for the impact loading condition, it is clearly demonstrated that, when the rise time of the applied impact velocity is sufficiently short, a large tensile stress arises on the boundary of the internal surface of the tube. It is also found that the maximum value of the caused tensile stress on the boundary of the internal surface becomes larger when the rise time becomes shorter, and when the ratio of the thickness of the tube to the outside diameter becomes larger than about 0.3.