To reduce the space of a mounting space, and to improve removal efficiency of metal ions.

In a common rail type fuel injection system, a fuel supply system for supplying fuel from a fuel tank to an engine is mounted with a metal ion removal filter 6. The metal ion removal filter 6 is connected to an upstream end (fuel suction port) in a fuel flow direction of a supply pipe. More specifically, the metal ion removal filter 6 is immersed in fuel stored in a fuel storage chamber of the fuel tank. Further, an inlet port and an outlet port of a filter case 8 are mounted with many ion exchange resin beads 7 capable of removing metal ions contained in fuel stored in the fuel storage chamber of the fuel tank and ion exchange resin nonwoven fabrics 11, 12.