FUEL INJECTION SYSTEM OF INTERNAL COMBUSTION ENGINE

PROBLEM TO BE SOLVED: To maintain sufficient sealing performance between a fuel injection valve and a fuel supply pipe even in a case where high fuel pressure is generated in the fuel supply pipe such as a delivery pipe. SOLUTION: When a delivery pipe body 70A and an adapter 70B are integrated with each other, an insertion hole of an insertion portion 61 of a fuel injection valve 60 is formed from an insertion hole 75 of the adapter 70B toward an insertion hole 74 of the delivery pipe body 70A. Further, in the midway of this insertion hole, an enlarged diameter portion 76 is formed, where an O-ring 80 for sealing fuel and backup rings 81, 82 are housed. According to the configuration of thus mounting the O-ring 80 to the enlarged diameter portion 76, a small pressure-receiving face a1 can be formed. Therefore, a high performance of the O-ring 80 is ensured even in the case of high fuel pressure.