IN-VEHICLE SYSTEM AND IN-VEHICLE ECU

An in-vehicle system includes: a first in-vehicle device installed in a vehicle; a second in-vehicle device controlled in accordance with a signal output from the first in-vehicle device; a first in-vehicle ECU communicably connected to the first in-vehicle device and the second in-vehicle device by signal lines; and a second in-vehicle ECU communicably connected to the first in-vehicle device and the second in-vehicle device by the signal lines. The first in-vehicle ECU and the second in-vehicle ECU are connected by a communication line of a type different from a type of the signal lines, and a communication path from the first in-vehicle device to the second in-vehicle device includes a first path relayed by the first in-vehicle ECU and a second path relayed by the second in-vehicle ECU.