An in-vehicle control system is mounted in a vehicle, which is connectable with a charging station through a charging cable and provided with a battery chargeable from the charging station through the charging cable. The vehicle includes a double-wire type communication line provided with a charger-side terminal circuit. The in-vehicle control system includes a first communication line and a second communication line, which are connectable to the communication line of the charging cable and provided with three terminal circuits. The in-vehicle control system further includes a first ECU and a second ECU, which are connected to the first communication line and the second communication line. When a charging plug is connected to a charging port, the first ECU and the second ECU validate the first terminal circuit and invalidate the second terminal circuit and the third terminal circuit.