To provide a communication system establishing synchronization between a wireless environment and a wire environment.

At a bridge 2, a comparing part 21 compares the cycles times with each other between a cycle time register 20-1 of a wire environment and a cycle time register 20-2 of a wireless environment. Then the cycle time of the register 20-2 is corrected according to the result of the said comparison, and the cycle times of cycle time registers 30-1 and 30-2 of the nodes 3-1 and 3-2 are corrected according to the corrected cycle time of the register 20-2. The synchronization is esterblished a cycle start packet among the cycle times of cycle time registers 10-1, 10-2 and 20-1 of the wire environment.