PURPOSE: To efficiently perform retrieval processing by setting plural retrieval keys, and performing single retrieval key designation and plural retrieval key designation in the retrieval processing of data.

CONSTITUTION: A corresponding retrieval key file is recognized from an inputted retrieval key value(step 11), and conformed retrieval key data is read by a designated retrieval key(step 12), and rough information is displayed on a retrieval terminal(step 13). When the display request of retrieval key data from the following retrieval terminal is further issued(step 14), repetitive display is performed starting from the retrieval key data following the one read in last time, and a data file is read with a decided retrieval key, then, information is displayed. Therefore, it is possible to perform various kinds of key retrieval and to shorten retrieval time by providing the key file dedicated for retrieval processing.