A transmitter/receiver circuit includes secondary batteries connected in series, a first protection circuit in a high voltage side of the secondary batteries and including a transmitter circuit increasing a voltage of a binary signal to a level that is a first voltage higher than an anode voltage of a first secondary battery connected to the first protection circuit, and a second protection circuit in a low voltage side of the secondary batteries and including a receiver circuit that receives the binary signal from the transmitter circuit via a wiring and including a shift part decreasing the voltage of the binary signal to a level that is a second voltage lower than a cathode voltage of a second secondary battery connected to the second protection circuit, and a detection part that determines that the wiring is disconnected when the voltage of the binary signal is lower than a reference voltage.