The copy of data in two directions is realized without fixing a copy direction to one direction between storage device systems which constitute a copy pair. In storage device systems which constitute a copy pair, a data consistency holding control part is disposed. The data consistency holding control part operates so as to write write-in data to a logical volume which forms the copy pair into a physical storage device after cache part has waited for more than a predetermined time from the corresponding reception time, in such a manner that, when write-in data which was received from a superior device and write-in data which was received from another storage device system through DKCI/F are written into the same storage location of the physical storage device in an overlapped manner, they are written in the order of the time of reception on which the write-in data was received from a superior device.