Speech telephones are incorporated in a LAN, and, for example, when a voice telephone 5 communicates with another voice telephone 8, call control is performed through exchange of information between a PC 1 and a PC 4, juxtaposed with the voice telephones, respectively, via a LAN hub 10, a LAN switching unit 50, and a LAN hub 20. Speech data of the respective telephones 5, and 8 are packetized in the data block of a MAC frame by concentrators 30, and 40 for voice telephones, respectively, and relayed to LAN-SW interfaces 30a, and 40a. Frames having a function of absorbing fluctuation are applied to the data block of the interfaces 30a and 40a. Respective voice data packetized according to the MAC address of the MAC frame are delivered to the voice telephones 5, and 8, respectively, via the LAN switching unit 50, and the concentrators 30, and 40 for voice telephones.