An information transmission system comprising: a first station (10; 10') connected to a data source supplying data codes (M1/ M2/ M3) thereto at irregular interval, and including a modulating unit producing a modulated signal on the basis of said data codes (M1/ M2/ M3) through a modulating technique selected from the group consisting of differential phase-shift keying and frequency shift keying, and a data converting unit (13; 13A; 13A/ RT) connected to said modulating unit (11/ 12) for producing an output signal from said modulated signal; a second station (30; 30/ RR) supplied with said output signal of said data converting unit, and including a demodulating unit supplied with said output signal of said data converting unit for reproducing said data codes (M10/ M11/ M12) through a demodulating technique corresponding to said modulating technique; and a discriminating unit analyzing said output signal so as to determine said modulating technique employed in said modulating unit and supplying a control signal representative of said modulating technique to said demodulating unit so that said demodulating unit selects said demodulating technique from demodulation techniques respectively corresponding to said modulating techniques; and an information transmitting medium (20; NW1) provided between said first station and said second station, characterized in that said discriminating unit includes plural detectors (110/120, 130, 140) each assigned to one of said modulating techniques and determining whether or not an edge-to-edge interval of said output signal is unique to said one of said modulation techniques for producing a detecting signal representative of a positive answer or a negative answer, a signal generator (150, 160, 170, 180) connected to said plural detectors (110/120, 130, 140) and determining said demodulating technique on the basis of the answers supplied from said plural detectors (110/120, 130, 140) for supplying said control signal to said demodulating unit. a first station (10; 10') connected to a data source supplying data codes (M1/ M2/ M3) thereto at irregular interval, and including a modulating unit producing a modulated signal on the basis of said data codes (M1/ M2/ M3) through a modulating technique selected from the group consisting of differential phase-shift keying and frequency shift keying, and a data converting unit (13; 13A; 13A/ RT) connected to said modulating unit (11/ 12) for producing an output signal from said modulated signal; a second station (30; 30/ RR) supplied with said output signal of said data converting unit, and including a demodulating unit supplied with said output signal of said data converting unit for reproducing said data codes (M10/ M11/ M12) through a demodulating technique corresponding to said modulating technique; and a discriminating unit analyzing said output signal so as to determine said modulating technique employed in said modulating unit and supplying a control signal representative of said modulating technique to said demodulating unit so that said demodulating unit selects said demodulating technique from demodulation techniques respectively corresponding to said modulating techniques; and an information transmitting medium (20; NW1) provided between said first station and said second station, characterized in that said discriminating unit includes plural detectors (110/120, 130, 140) each assigned to one of said modulating techniques and determining whether or not an edge-to-edge interval of said output signal is unique to said one of said modulation techniques for producing a detecting signal representative of a positive answer or a negative answer, a signal generator (150, 160, 170, 180) connected to said plural detectors (110/120, 130, 140) and determining said demodulating technique on the basis of the answers supplied from said plural detectors (110/120, 130, 140) for supplying said control signal to said demodulating unit.