Abstract: To permit transmission of traffic information by amplitude modulation in the medium wave band without disturbing audio signals being broadcast, a stereo pilot tone of frequency f.sub.pt below audible range is generated, as well as first and second sinusoidal signals of f.sub.1 =m.sub.1 /n.multidot.f.sub.pt and f.sub.2 =m.sub.2 /n.multidot.f.sub.pt, in which m.sub.1, m.sub.2, and n are different integers. The carrier is modulated by the stereo pilot tone and the first and second sinusoidal signals in such a manner that the phases thereof are different and further, when added, they do not essentially exceed the amplitude of the stereo pilot tone.