Bicycle Communication Adapter

To provide a communication adapter that can supply a signal and electric power from a management system to a bicycle electrical system in which a plurality of electric devices can be connected using power line communication. The communication adapter 40 can connect a bicycle electrical system 7 in which a plurality of electric devices can be connected using power line communication to a management system 50 configured to manage the bicycle electrical system. The communication adapter has a second controller 45 and a voltage step-up circuit 42. The second controller 45 converts a signal outputted from the management system 50 into a signal compliant with a power line communication standard. The voltage step-up circuit 42 raises a voltage supplied from the management system 50. The second controller 45 superimposes the converted signal onto the raised voltage produced by the voltage step-up circuit 42.