PURPOSE: To realize the excellent method for digital mobile communication in which synchronization between connected devices is established even when radio communication between the connected device is difficult and no exclusive receiver is needed.

CONSTITUTION: An exchange station 1 is provided with a means sending timing information to a connected device, a delay buffer adjusting a communication start time, and a means which detects the timing information returned from connected devices 3a, 3b through communication lines 5a, 5b and controls a delay of the delay buffer based on the result of detection.