An information retrieval system in which various information is indexed synthetically into such relations as the synonym, the broader term and the narrower term to provide a thesaurus and the words are coded to provide a keyword relation table, an index table and a word table each stored in a memory device respectively so that the desired information retrieval operation may be conveniently performed with use of a computer system. Particularly, a memory capacity even for memory of the thesaurus of large scale may be reduced considerably with simplification of the computer system.