PURPOSE: To retrieve a picture in a short time by dividing picture data on the respective pages of a document, storing them, and only reading the picture data of a block designated out of the divided picture data on the respective pages when the document is retrieved.

CONSTITUTION: When the document is registered, the picture of the document is read in units of a page, a block controller 25 divides the picture data on a memory 23 according to the dividing command of the picture, and transmits them from a communication processor 21 to a center device 10 in units of a block together with information concerning the number of division. The data are once stored into a memory 18, and next, successively written to an optical disk 13 in units of a block by the control of a block controller 24. When the document is retrieved, a data processor 17 of the center device 10 defines the picture point of a target document according to the retrieve information, the picture data for one page are read from the optical disk 13 together with the information concerning the number of division, and only the picture data of the necessary block are fetched. Thus, the data quantity to transfer a network is decreased, and the retrieving time can be shortened, as well.