Three-dimensional unsteady blood flows through the artery with a small side branch were analyzed numerically using the finite element method. Our main attention was paid to the model that had a large branch angle (>90°) between the trunk and side branch. This arterial geometry is easily found in the actual arterial system. In this study, the arterial wall was assumed to be rigid and the non-Newtonian effect of blood was not taken into consideration. The calculated results are summarized as follows : 1) The branch angle does not have a strong effect on the flow rate through the side branch. 2) In the case of large branch angle, the still standing stagnation point appears near the outer wall of side branch. Moreover, this still standing stagnation point has an effect to increase the value of WSSG.