A file system includes a processing device that processes first data with at least one of a copying function to read image data of an original document and record the read image data on a sheet, a transmitting function to send and receive image data and/or character data via a communication line, and a recording function to record received image data and/or character data on a sheet. The file system also includes a memory device to store the first data processed by the processing device, an identity determination device to determine an identity (i.e., similarity or relation) between the processing data and second data stored in the memory device, and a storage management device stores the first data into the memory device on the basis of a result of a determination made by the identity determination device. The storage management device cancels the storage of the first data into the memory device when the identity determination device determines that the first data is identical to second data stored in the memory device. The identity determination device determines the identity between the first data and the second data stored in the memory device based upon information of processes with which the first data has been processed with the processing device. The information of processes includes information of an original document associated with the first data.