PURPOSE: To provide a multiplex transmitter in which a voice and the modulated signal of digital data can be simultaneously multiply transmitted with in the prescribed frequency band of a transmission path, and the articulation and resolution of the voice signal can be improved.

CONSTITUTION: At the time of simultaneously transmitting the modulated signal and the voice signal, a transmission side switching circuit 21 and a reception side switching circuit 23 are switched to a filter side contact (b), and the transmission frequency bands of the voice signal and the modulated signal are separated. At the time of transmitting only the voice signal, the switching circuits 21 and 23 are switched to a by-pass side contact (a), and the transmission frequency band of the voice signal is enlarged. A time synchronizing circuit 25 outputs a switching signal.