To provide a method for calculating the thickness direction and thickness of solid elements and an apparatus for calculating the thickness direction and thickness of solid elements especially for use in a fluid flow analysis using solid elements and in a structural analysis based on the fluid flow analysis results.

The apparatus has:a means for acquiring free faces of a solid model, an evaluation direction decision means for determining six search directions, and a distance calculation means for calculating a point of minimum distance on the free face of the solid model in each search direction from a reference position of each solid element of the solid model. The thickness and distance are evaluated for three sets of opposite search directions to calculate the thickness and thickness direction.