PURPOSE: To improve durability and reliability and to improve assembling ability by preventing breakage of an insulation cover.

CONSTITUTION: A fuel injection device comprises a fuel injection valve to inject fuel directly to the combustion chamber of an internal combustion engine; and an ignition plug formed integrally with the injection valve. A cap sub-assembly 23 having an insulation cover 13 located between a valve seat 5, in which the valve 10 of a fuel injection valve is incorporated and which is the central electrode of an ignition plug, and a cap 11 having the earth electrode 12 of the ignition plug is assembled in a housing 20 in such a state that an regulating plate 22A to effect fine-regulation of the opening closing stroke of the valve 10 through adjustment of a plate thickness (t) is located. A contact member 18A made of a metal making contact with the regulating plate 22A is arranged at the cap sub-assembly 23 to prevent contact between an insulation cover 13 and a regulation plate 22A.