A fuel supply apparatus is provided for an intake manifold and a fuel injection system that can be easily and reliably mounted together by a mounting structure, even when the intake manifold has an integrated design in which air intake branches curve steeply upward from a downward side to an upstream side. With this fuel supply apparatus, the fuel injection system is mounted with coupling bolts on the top surface of the outer wall of the downstream portion of the intake manifold. The threads of the bolts engage internal threaded bores in the fuel injection system. The heads of the bolts are disposed on a reverse side of a top surface of an outer wall of the intake manifold, with internal threaded bores of the fuel injection system being disposed on a side of the top surface of the outer wall of the intake manifold.