1. A search processing method, comprising: providing a system that includes an index search controller, a string pattern matching controller, an index search unit to carry out an index search using a search index before a document update, a string pattern matching unit having document contents after said document update, and a storage device; said index search controller to cause said index search unit to carry out said index search relating to a search request, and obtaining and storing into said storage device, a first list of document IDs of pertinent documents; said string pattern matching controller to cause said string pattern matching unit to carry out a character string pattern matching relating to said search request for said document contents after said document update, and obtaining and storing into said storage device, a second list of document IDs of pertinent documents; said string pattern matching controller to generate a search result for said search request by removing from said first list, document IDs of documents updated by said document update, to generate a third list of document IDs obtained by said removing, and to generate a sum-set of said second list and said third list, wherein said search result includes said sum-set of said second list and said third list; and said string pattern matching controller to output said search result.