An assembly process apparatus includes an assembly robot for assembling parts to a workpiece which is a main body, a part supply apparatus for supplying parts to the workpiece, a work pallet for supplying workpieces to an assembly station of the assembly robot, and a tool pallet for supplying assembly process modules interchangeable with respect to the assembly robot. The part supply apparatus is made up of a plurality of part supply modules interchangeable with respect to the assembly robot. With the assembly process apparatus as one unit, it is constructed to assemble parts one unit only or with a plurality of units combined. Accordingly, an assembly process apparatus achieves excellent productivity with which it is possible to expand or cut line equipments easily according to production volume, and it is possible to achieve utilization of surplus assembly robots.