A D channel packet communication system and a method of D channel packet communication in a private branch exchange allows connection control information conversion for a D channel packet which passes through a network, without call processor processing. The connection control information of D channel packet, such as a TEI, a LCGN and LCN, independently allocated for a communication between a packet terminal and a PBX (line side), and for a communication between the PBX and a network (network side) is adequately converted by the conversion control unit. The conversion control unit has first conversion information based on conditions of the connection control information to be used at the line side and at the network side, and derives second conversion information corresponding to each packet communication based on the first conversion information and connection control information contained in a packet of each packet communication. The D channel packet is discriminated by a switching control unit and input to the conversion control unit, and then, the connection control information contained in the D channel packet received from one side is converted by the second conversion information and transferred as the packet to the other side.