An in-vehicle device is an in-vehicle device mounted on a vehicle and to provide with a driving unit, the device including: a control unit controlling the driving unit; and a communication unit for communicating with an in-vehicle ECU to be mounted on the vehicle, in which when an inhibition event for inhibiting diagnosis processing of the driving unit is detected at the time of performing the diagnosis processing, the control unit outputs a detection result notification indicating that the inhibition event is detected to the in-vehicle ECU through the communication unit.