Abstract: A buffer storage system provided between an instruction executing portion and a main storage for enabling the instruction executing portion to quickly fetch and store date in a frequently-accessed address area. The buffer storage system includes a plurality of buffer storages each storing the same data; and a move-out buffer register provided between the plurality of buffer storages and the main storage. When data held in the buffer storages is required to be moved out to the main storage, a part of the data to be moved out is transferred from each of the plurality of buffer storages to a corresponding portion of the move-out buffer register, and then the data is transferred from the move-out buffer register to the main storage.