A communication system that is configured to transmit data from a plurality of transmission devices (10, 20, 40) to one reception device via a pair of signal lines, each of the transmission devices (10, 20, 40) comprising: a mode controller (11, 21, 41) that is configured to control a transmission mode; a transmission data generator (14, 24, 44) that is configured to generate the data in accordance with the transmission mode controlled by the mode controller (11, 21, 41); and a data transmitter (15, 25, 45) that is configured to transmit the data generated by the transmission data generator (14, 24, 44) to the reception device, in a case where the transmission mode of a first transmission device of the plurality of the transmission devices (10, 20, 40) is an High Speed, HS, mode, the mode controller (21, 41) of any second transmission device (20, 40) of the plurality of the transmission devices (10, 20, 40) is configured to turn the transmission mode of the second transmission device (20, 40) to a termination mode in which a pair of output terminals (40A, 40B) of the second transmission device (20, 40) is terminated, wherein each of the data transmitters (15, 25) includes: a terminator resistor that is configured to turn on and off termination of the pair of output terminals (40A, 40B) coupled to the pair of signal lines, and a termination controller (PHY-FSM) that is configured to detect the transmission mode of other transmission devices (10, 20, 40) on a basis of a voltage of the pair of output terminals (40A, 40B) and to control on and off of the terminator resistor on a basis of a result of such detection. a mode controller (11, 21, 41) that is configured to control a transmission mode; a transmission data generator (14, 24, 44) that is configured to generate the data in accordance with the transmission mode controlled by the mode controller (11, 21, 41); and a data transmitter (15, 25, 45) that is configured to transmit the data generated by the transmission data generator (14, 24, 44) to the reception device, in a case where the transmission mode of a first transmission device of the plurality of the transmission devices (10, 20, 40) is an High Speed, HS, mode, the mode controller (21, 41) of any second transmission device (20, 40) of the plurality of the transmission devices (10, 20, 40) is configured to turn the transmission mode of the second transmission device (20, 40) to a termination mode in which a pair of output terminals (40A, 40B) of the second transmission device (20, 40) is terminated, wherein each of the data transmitters (15, 25) includes: a terminator resistor that is configured to turn on and off termination of the pair of output terminals (40A, 40B) coupled to the pair of signal lines, and a termination controller (PHY-FSM) that is configured to detect the transmission mode of other transmission devices (10, 20, 40) on a basis of a voltage of the pair of output terminals (40A, 40B) and to control on and off of the terminator resistor on a basis of a result of such detection. a terminator resistor that is configured to turn on and off termination of the pair of output terminals (40A, 40B) coupled to the pair of signal lines, and a termination controller (PHY-FSM) that is configured to detect the transmission mode of other transmission devices (10, 20, 40) on a basis of a voltage of the pair of output terminals (40A, 40B) and to control on and off of the terminator resistor on a basis of a result of such detection.