1. A search processing method, comprising: causing an index search unit for carrying out an index search using a search index before a document update to carry out said index search relating to a search request, and obtaining a first list of document IDs of pertinent documents; causing a string pattern matching unit having document contents after said document update to carry out a string pattern matching relating to said search request for said document contents after said document update, and obtaining a second list of document IDs of pertinent documents; and generating a search result for said search request by using said first and second lists and a third list of document IDs of documents relating to said document update.