PURPOSE: To obtain a synchronizing multiplexer to synchronizingmultiplex a low order group signal without changing a transmitting speed by changing the attribute of a frame bit added to the low order group signal for the signal.

CONSTITUTION: In a case where the frame constitution of two inputted low order group signals CH1 and CH2 and the frame constitution of a synchronized multiple signal are made as shown on a figure, when respective frame bits of the low order, group signals CH1 and CH2 are an F and an F' and an information bit is indicated as an I, respective polarities of the frame pulses of the frame bit F and frame bit F', are set so as to be mutually reverse. In such a way, at a receiving side, a separation into two channels can be executed based on a difference in the frame bits.