Relaying device, network system, and network system controlling method

The first relaying device uses the first port (the second relaying device) for the first priority in the first selecting mode, and uses a port other than the second port (the third relaying device) for the second priority. The first relaying device uses the first port for the first priority and uses the second port for the second priority, in the second selecting mode. In a case where the selecting mode is the first selecting mode, the power mode of the third relaying device is the first power mode wherein the power consumption is relatively small. In a case where the selecting mode is the second selecting mode, the power mode of the third relaying device is the second power mode wherein the power consumption is relatively high.