PURPOSE: To execute the data transfer with high reliability by maintaining a setting condition with a first SYNCOUT signal at a prescribed time point even by a string controller even when an interface cable length is changed and a delaying time is changed.

CONSTITUTION: The data transferred from a main processor 11 are recorded through a control device 12 and string rollers 13 (13a, 13b) to magnetic disk devices 14a and 14b. The delaying time of an SYNOUT signal fed back and inputted by an SYNCIN generating circuit 50 in an SYNC control circuit 140 of the controller 13 is measured and the output of the SYNCIN signal is inhibit- controlled in accordance with the delaying condition. In such a case, even when the interface cable length is changed and the delaying time is changed, the overflow of buffers FFA28 and FFB29 is not generated, and the setting condition by the first SYNCOUT signal can be maintained by the buffer FFA28 or FFB29 at the prescribed time point.