To enable an in-vehicle device to perform correct determination even when there is congestion in communication.

An in-vehicle device 10 which determines traffic condition around a vehicle, comprises: detection means (radar device 16 and imaging device 17) which detects objects around the vehicle; communication means (communication unit 11) which receives traffic information by radio communication with another vehicle or a center device; determination means (control processing unit 13) which determines whether there is congestion in communication by the communication means; and determination means (control processing unit 13) which determines surrounding traffic condition by prioritizing a detection result by the detection means when the determination means has determined that there is congestion in the communication, otherwise determines surrounding traffic condition on the basis of both detection result by the detection means and traffic information acquired by the communication means.