To provide an assembly line system which can conform to the operating speed of each operator at which the operator assembles workpieces, to thereby improve the working efficiency thereof.

The assembly line system is comprised of an automotive carriage 1, a main traveling line 2, a plurality of branched traveling lines 3, limit switches 8, a main computer 10, and a destination designating device 15. The automotive carriage 1 can move from the main traveling line 2 to an arbitrary one of assembly work stations D via the branched traveling line 3 corresponding to the station. The limit switches 8 are arranged in the respective assembly work stations D and activated upon the movement of the automotive carriage 1 after the completion of the assembly at the assembly work stations D. The main computer 10 controls priorities to each assembly work station based on the order of reception of operating signals from the limit switches 8. The destination designating device 15 designates the assembly work station D corresponding to the operating signal, i.e., the destination of the automotive carriage on which a plurality of assemblies and a workpiece in which the assemblies are incorporated are mounted based on the priorities from the main computer 10.