PURPOSE: To improve a retrieving efficiency by updating and utilizing an already prepared machine M at the time of deleting character strings to be retrieved.

CONSTITUTION: The machine M for the plural pairs of character strings to be retrieved is prepared (S1), and when the character strings to be retrieved are deleted (S2), state transition data corresponding to the deleted character strings are deleted from the already prepared machine M (S3). When the transition is not defined, the state operating transition to the deleted state transition data is searched, and the already prepared destination of transition data are changed (S4). Then, when a retrieving pointer reaches the state, the deleted character strings are deleted from the character strings to be retrieved (S5), and a text is retrieved by using the updated machine M (S6).