Abstract: An in-vehicle control system mounted on a vehicle includes: a first control unit; a second control unit connected to the first control unit via a first communication path; and a third control unit connected to the second control unit via a second communication path. The second control unit has an internal communication path configured to be able to connect the first communication path and the second communication path and connects the first communication path and the second communication path via the internal communication path when the vehicle is in a predetermined operation state.

Abstract: An arithmetic device includes a first arithmetic chip configured to perform arithmetic processing for realizing driving assistance functions of a vehicle, and a second arithmetic chip configured to perform arithmetic processing for realizing the driving assistance functions of the vehicle, wherein, among the driving assistance functions, second functions realized by the first arithmetic chip along with the second arithmetic chip includes a function of providing at least some of first functions realized without depending on arithmetic processing of the second arithmetic chip in a state in which a task imposed on a driver has been reduced, as compared to the first functions.