An in-vehicle system has a first transmitting antenna that is disposed in a substantial center in a front portion inside a vehicle, a second transmitting antenna that is disposed in the substantial center in a rear portion inside the vehicle, a third transmitting antenna that is disposed in a side surface near a driver seat or a passenger seat of the vehicle, a transmission controller that controls transmission of a first signal or a second signal from the first to third transmitting antennas, the second signal disturbing reception of the first signal, and a receiving antenna that receives a response signal, the response signal being transmitted from a portable device receiving the first signal transmitted from the first to third transmitting antennas.