A relaying device, comprising: a network communication unit connected to a communication network and communicating with a plurality of terminal devices and other relaying devices over the communication network; a table storing a transfer destination of an audio signal of a group communication which is communication with terminal devices belonging to a group; and a control unit configured to control the group communication operating itself in a master mode or in a slave mode, wherein in the master mode, the table stores subordinate terminal devices which are both belonging to the group and which are subordinate to the relaying device and slave relaying devices, which are said other relaying devices and set to the slave mode, as the transfer destination, wherein each of said slave relaying devices is communicating with its own respective subordinate terminal devices belonging to the group, in the slave mode, the table stores subordinate-group terminal devices which are both belonging to the group and which are subordinate to the relaying device and a master relaying device which is another relaying device, comprised in said other relaying devices, set to the master mode as the transfer destination, in the master mode, the control unit is configured to transfer, based on the table, an audio signal of the group communication received from one of the subordinate terminal devices of the relaying device to the other of the subordinate terminal devices of the relaying device excluding the transmitting subordinate terminal device of the relaying device and to the slave relaying devices and also to transfer, based on the table, an audio signal of the group communication received from one of the slave relaying devices to the other slave relaying devices excluding the transmitting slave relaying device and to all the subordinate terminal devices of the relay device, and in the slave mode, the control unit is configured to transfer, based on the table, an audio signal of the group communication received from one of the subordinate terminal devices of the relaying device to the other of the subordinate terminal devices of the relaying device excluding the transmitting subordinate terminal device of the relaying device and to the master relaying device, and also to transfer, based on the table, an audio signal received from the master relaying device to all the subordinate terminal devices of the relaying device. a network communication unit connected to a communication network and communicating with a plurality of terminal devices and other relaying devices over the communication network; a table storing a transfer destination of an audio signal of a group communication which is communication with terminal devices belonging to a group; and a control unit configured to control the group communication operating itself in a master mode or in a slave mode, wherein in the master mode, the table stores subordinate terminal devices which are both belonging to the group and which are subordinate to the relaying device and slave relaying devices, which are said other relaying devices and set to the slave mode, as the transfer destination, wherein each of said slave relaying devices is communicating with its own respective subordinate terminal devices belonging to the group, in the slave mode, the table stores subordinate-group terminal devices which are both belonging to the group and which are subordinate to the relaying device and a master relaying device which is another relaying device, comprised in said other relaying devices, set to the master mode as the transfer destination, in the master mode, the control unit is configured to transfer, based on the table, an audio signal of the group communication received from one of the subordinate terminal devices of the relaying device to the other of the subordinate terminal devices of the relaying device excluding the transmitting subordinate terminal device of the relaying device and to the slave relaying devices and also to transfer, based on the table, an audio signal of the group communication received from one of the slave relaying devices to the other slave relaying devices excluding the transmitting slave relaying device and to all the subordinate terminal devices of the relay device, and in the slave mode, the control unit is configured to transfer, based on the table, an audio signal of the group communication received from one of the subordinate terminal devices of the relaying device to the other of the subordinate terminal devices of the relaying device excluding the transmitting subordinate terminal device of the relaying device and to the master relaying device, and also to transfer, based on the table, an audio signal received from the master relaying device to all the subordinate terminal devices of the relaying device.