To provide a fuel injection device for an internal combustion engine embodied on the in-line system in which a fuel pump is installed in fuel piping to put a fuel tank in communication to a fuel injection valve, free of limitation on the layout of a fuel pump of non-displacement type.

The fuel injection device of the internal combustion engine is structured so that the motor-driven fuel pump P of non-displacement type is installed inside an outer case 20, a suction hole 6 of the pump P is open to a fuel influx chamber 30 formed in the outer case 20, and that a pump discharge hole 14 is connected with a fuel discharge hole 26 in the outer case 20. A fuel return chamber 31 is formed between the inside surface of the outer case 20 and the peripheral surface of the pump P and is connected with the fuel influx chamber 30 and with a fuel returning hole 24. The outer case 20 including the pump P is positioned below the fuel tank T, and the fuel influx chamber 30 is connected with the bottom of the tank T through a fuel influx hole 21 and a fuel influx passage 40, and the fuel discharge hole 26 is connected with a fuel injection valve J through a fuel discharge passage 41 while the fuel returning hole 24 is connected with the tank T through a fuel returning passage 43.