An assembly apparatus includes a retainer, a position measurement device, and a machining device. The retainer is configured to hold an assembly. The position measurement device is configured to measure a difference between an intended machining position and an actual machining position of a first coupling hole in a first assembly component. The first coupling hole is capable of being coupled to the assembly. The machining device is configured to form a second coupling hole capable of communicating with the first coupling hole in the assembly based on a reference position set on the assembly and the difference.