Prestroke Adjustment Method for Fuel Injection Valve

Provided is a prestroke adjustment method for a fuel injection valve capable of reducing variations in a prestroke amount regardless of the level of machining accuracy of a component. The prestroke adjustment method adjusts a prestroke amount D2 of a fuel injection valve 1 including a gap forming member 50 that forms a gap G2 defining a prestroke between a valve member 30 and engagement portions 33a and 423a of a movable core 42 by a second portion 52a abutting on the movable core 42 in a state where a first portion 51a is positioned at a reference position 33b of the valve member 30. In the prestroke adjustment method, a load L in the direction from the first portion 51a toward the reference position 33b of the valve member 30 is applied to the gap forming member 50 assembled to the valve member 30 to plastically deform the gap forming member 50, thereby shortening the relative length between the first portion 51a and the second portion 52a and setting the prestroke amount D2 to the target value T2.