Abstract: A voice packet multiplexer with a voice transit switching function, which is connected to a PBX in an office. It detects an originating logical channel according to digits sent from the PBX, and sets, when transmitting a signal packet or voice packet, the detected originating logical channel in its address field. It also stores an originating logical channel while receiving a packet from a packet communication network. It further extracts an office number from a received packet containing the digit information, makes a decision whether the office number is the number of its own office or of another office, and retrieves, if it is of the another office, a terminating logical channel for establishing connection with that office. To carry out the voice transit switching after determining the terminating logical channel, it transmits a packet after translating its address field into the terminating logical channel or into the originating logical channel.