A method and an apparatus are provided for merging two meshes whose density differs from each other so as to avoid unnatural appearance. A first mesh and a second mesh that differ from each other in density are merged by the following procedure. Edge length of a portion that becomes a boundary between the first and second meshes is determined, size of a first group of polygons including the edge of the portion is determined based on the determined length and size of a second group of polygons is adjusted so that an adjustment ratio is smaller as a distance between a position of each of the second group of polygons and the portion is greater, the first and second group of polygons being part of polygons structuring the first and second meshes, and the first and second meshes in each of which the polygons are adjusted are merged.