An electronic control apparatus includes a first arithmetic processor and a second arithmetic processor that is communicably connected to the first arithmetic processor. The second arithmetic processor includes a controller configured to (i) shift to a rewriting wait state after outputting a request signal that requests a program rewriting to the first arithmetic processor, and (ii) release the rewriting wait state and shift to a program rewriting process after a predetermined wait time that allows the first arithmetic processor to shift to the program rewriting process elapses after outputting the request signal.