An in-vehicle sensor (1) mounted on a vehicle VE and connected to a communication bus CAN including a bus connection connector (40) for connection to the CAN and external terminals (T3, T4) for communication, and one or a plurality of external terminals (T5, T6) for setting each brought into either of a first connection state not connected to any potential and a second connection state connected to a ground potential GND; a judgment section S1-S4, S5-S7 for setting whether the connection state is the first connection state or the second connection state; and an identifier setting section S8 which sets an identifier ID of the in-vehicle sensor (1) used on the communication bus CAN based on the judged connection state(s) for setting of the one or plurality of external terminals (T5, T6).