1. A source-program processing method for processing a source program on a computer comprising: dividing code of the source program into components and extracting a group of components; comparing every two components among the extracted group of components, thus obtaining a comparison index for the two components; classifying the extracted group of components in a tree-like hierarchical structure, based on the extracted group of components and the comparison index for every two components, the hierarchical structure having nodes each possessing three types of information which are the comparison index for every two components, the number of children of each node and the number of leaves of each node; retrieving two types of information, which are the comparison indices and at least one of the number of children of each node and the number of leaves of each node, on each node in the tree-like hierarchical structure and carrying out a specific computation based on the information; and quantitatively evaluating functional redundancy of the source program based on the total result of the specific computation for the nodes in the tree-like hierarchical structure.