To provide a fuel injection system including a subtank of an alternative pathway which is provided separately from a main tank of a fuel tank, in which fuel switching can be performed without causing the deterioration of oil sealing function when the residual fuel in the fuel tank is decreased.

The fuel injection system includes a drive shaft 1, a feed pump 3 which has a suction-side fuel passage 71 and a discharge-side fuel passage 72, an oil seal 62 of the drive shaft, and a bearing 61 which supports the drive shaft. In the fuel injection system, the fuel inhaled by rotation of the feed pump 3 is fed out to a pump house and the fed-out fuel is further pressurized. The suction-side fuel passage 71 includes a fuel inlet-side path 79 which directly introduces the fuel in the fuel tank, and a fuel recovery path 73 which opens in an inner peripheral surface 2d of a pump housing 2 between the oil seal 62 and a first bearing 61a arranged in the vicinity of the oil seal 62. The fuel recovery path 73 is provided with a check valve 80 which intercepts communication when the fuel pressure in the fuel inlet-side passage 71 is higher than that in the fuel recovery path 73.