To reduce noise of an engine caused by looseness of a gear by providing with a damping device for exhibiting action for damping twist exciting force generated by a fuel system while injection fuel, in the damping device connected to the driving gar of the fuel system.

A fuel injection device 10 is provided with a driving gear 12 driven by gear trains 14 which are engaged with each other, and thereby, twist exciting force is generated in a process for generating high injection pressure by a fuel injection device 10 so as to transfer its exciting force to a driving gear 12. A damping device 16 is provided aside the driving gear 12 of a fuel system so as to reduce shock force caused by twist vibration and gear back lash. The damping device is formed in such a constitution that a free mass element may be freely stored through a viscous fluid in an outer housing, and arranged in a recessed part formed on the side surface of the driving gear 12.