A control module cluster unit which enables high-speed communication by restraining the effect of noise, for constituting a high-reliability vehicle control system including a plurality of control modules each having control functions modularized in accordance with control objects, such as ECU for engine control, ECU for ABS, etc. in conventional use, an input/output module, common modules, and communication modules collectively mounted in one casing are so constituted as to enable mutual communication through a common bus on a mother board. A signal inputted in the input/output module is distributed to each module requiring the input signal through the mother board. The control module cluster unit also has a temperature sensor for detecting casing temperature and a power source for powering each of the modules. When detected temperature is abnormally high, the power source shuts down less important parts of the control module cluster units.