A vortex extraction apparatus includes: a first numerical data calculation section calculating, for each vertex of each of voxels into which the inside of a fluid space is split, first numerical data indicating whether the vertex is located inside or outside a vortex region in a fluid; and a text data creation section determining the size of the vortex region around a center line of the vortex based on the first numerical data, and creating text data indicating the center line and the size. The apparatus further includes a polygon count reduction processing section counting the number of polygons defining a surface of the vortex region and each including an isosurface of the first numerical data, and integrating the voxels with new voxels into which the fluid space is roughly split until the number of polygons is not more than a set value, to decimate the first numerical data.