PURPOSE: To process a next retrieving request without waiting the end of preceding retrieval even if the retrieving requests are generated as being overlapped by storing the stored data of an optical disk temporarily in a magnetic disk device as looking ahead it in a lump by a document unit.

CONSTITUTION: When the retrieving request is generated from terminals 5, 6 for retrieval, a collective optical disk control device 2 sets the optical disk (for instance, B) the retrieving request to which is accepted at first in an optical disk drive 11 by using an accessor 12. After that, the data is read out from this optical disk B. This read-out data is transmitted to the terminals 5, 6 for retrieval of a retrieval requesting origin, and simultaneously, all the document data of the retrieval requested object consisting of plural pages are looked ahead in a lump, and are stored temporarily in the magnetic disk device 3. Thus, even if the requests for the different disks more than the number of the optical disk drives 11 are generated, it becomes possible to access the next optical disk without waiting until the request accepted at first is finished.