PURPOSE: To execute the retrieval processing at a high speed with regard to the pattern retrieval processing system for setting a pattern containing an arbitrary pattern of variable length as a retrieval object, and retrieving an expansion position of this pattern contained in text information.

CONSTITUTION: The system is constituted so that in the case a pattern which is a retrieval object contains one or plural pieces of arbitrary patterns of variable length, the retrieval processing is executed by first decomposing its pattern into sub-patterns and retrieving an expansion position of those sub-patterns, and subsequently, specifying that which holds a sequence relation and a position relation of the sub-patterns, in combination of the expansion position of those sub-patterns.