1. A stress analysis method, comprising: dividing, on a computer, by using a division unit, an inside of a chip into a plurality of analysis areas; deriving, by using a composite property derivation unit, a composite property into which physical property values of a plurality of materials included in an analysis area are compounded, about each of the plurality of analysis areas on the basis of wiring structure data for each of the plurality of analysis areas, the composite property being derived by compositing a physical property value of a first material of the plurality of materials and a physical property value of a second material of the plurality of materials at a ratio on the basis of a wiring coverage; and creating, by using a stress analysis unit, a three-dimensional model of a finite element method which uses each analysis area as an element, to apply the composite property to each element, and to perform a stress analysis.