A stress estimating system includes a polygon data input unit of polygon data modeling a vascular wall, an interactive analysis condition setting unit for setting the tensile force acting on the vascular wall boundary, blood pressure and constraint estimated as proper on the boundary, a stress analysis unit for obtaining two-dimensional stress by solving a mechanical equilibrium equation with respect to the membrane stress on a curvilinear surface of the vascular wall under the condition given by the polygon data input unit and the interactive analysis condition setting unit, and an interactive visualization unit for displaying a distribution of a stress component designated by a system user. Without assuming any symmetry for the curvilinear configuration and stress distribution, a complicated stress distribution is estimated only out of the mechanical equilibrium equation with respect to membrane stress.