PURPOSE: To judge that an actual record is not a noise record without rerunning a retrieval expression and to shorten definite retrieval processing time by comparing each time of day added to each data base key in a subset and each time of day added to each actual record in a data base.

CONSTITUTION: A record for which data base update processing 11 is added or updated in stored in a data part accompanying the update of an index part, and the time of day is recorded in a time of day part as T2. On the other hand, in retrieval processing executed asynchronously with the data base update processing, in pre-retrieval processing 12, a data base key (DBK) corresponding to the actual record to hit as the result of running the retrieval expression is outputted to the subset, and the time of day is stored in the time of day part as T1. In definite retrieval processing 13, the actual record corresponding to the DBK of the subset is read from the data base and outputted, the respective times of day T1 and T2 are compared in order to decide whether this actual record is a noise or not, and when T1>T2, it is decided that the actual record is not the noise without rerunning the retrieval expression.