A substitution apparatus for installation in a vehicle in which a plurality of in-vehicle control apparatuses are implemented, the substitution apparatus including a control unit and a substitute unit. The control unit is configured to control the substitute unit based on transmission data transmitted from the in-vehicle control apparatuses, specify an abnormal in-vehicle control apparatus based on the transmission data, disable the specified abnormal in-vehicle control apparatus, and apply, to the substitute unit, a program for exhibiting functions otherwise normally executed by the specified abnormal in-vehicle control apparatus. The substitute unit is configured to substitute for the disabled in-vehicle control apparatus by executing the applied program.