To provide an automobile assembly system for eliminating the necessity to plan the production of power units, and solving the problem wherein the stock of the power units is held.

In the power unit assembly system for an automobile, vehicle body information of a vehicle body 31 being conveyed in order is read at a predetermined reading point in a vehicle body assembly line 2. A power unit assembly order plan for assembling the corresponding power unit 32 for the automobile in an automobile power unit assembly line 6 is generated based on the read vehicle body information. Then power unit assembly indicating information is generated on the basis of the generated power unit assembly order plan, and provided to the automobile power unit assembly line 6. Thus, the power unit 32 for the automobile is assembled in the power unit assembly line 6 in response to the specification of the vehicle body 31 which is actually produced and assembled in the vehicle body assembly line 2.