PURPOSE: To realize application of a hash method to retrieval of the added information and to retrieve the information at a high speed, by retrieving a 2nd storing means in case it is decided by an identification code that the information retrieved from a 1st storing means is not desired.

CONSTITUTION: A 1st storing means 111 stores the information including an identification code; while a 2nd storing means 121 stores the additional information including an identification code different from that of the 1st storing means. When the desired information is retrieved, a hashing means 131 uses a hash method to retrieve the means 111. An identification code deciding means 141 sends a retrieving instruction of the means 121 to the means 131 if it is decided that the retrieved information is not desired based on the identification code of said information. Thus the means 131 applies the hash method to retrieve the means 121.