PURPOSE: To add and mount simply a fuel restricting device to an in-line type fuel injection pump, and suppress supply of an excessive fuel injection amount by screwing a main body including the damper mechanism of a fuel restricting device into the screw hole of the in-line type fuel injection pump.

CONSTITUTION: In the case when a fuel restricting device 15 is added to an in-line type fuel injection pump 1 in order to change performance, a cap 10 is taken out from the screw hole 9 of a casing 7, and instead thereof, a male screw part 17 is screwed into the screw hole 9 to fix a main body 16, then the fuel restricting device 15 is mounted on the in-line type fuel injection pump 1. When a rack 6 is projected outward from a casing 4 till the position where the rack 6 comes in relation to a damper machanism 34 through the screw hole 9, a rack end abuts on a cap shaped nut 22. A piston 19 is pushed in the left direction by a force exceeding elastic force of a coil spring 26. At this time, the piston 19 is slid while throttling air in a piston stored chamber 18 by an orifice member 31, and pressurizing the air. Namely operation of the rack 6 is restricted by the damper mechanism 34 at the time of rapid acceleration or the like.