A transmitting case includes a first case half integrally formed on one side of a throttle body, and a second case half coupled to the first case half. A first assembly is constructed by disposing a final gear inside the first case half and securing it to one end of a valve shaft. A second assembly is constructed by mounting on the second case half an electric motor and an intermediate gear of a speed reduction device for transmitting the rotation of an output shaft of the electric motor to the final gear. Upon coupling of the first case half and the second case half, the intermediate gear and the final gear are meshed with each other. Thus, there is provided an engine intake control system having an excellent assemblability and an improved accuracy of throttle valve opening degree.