PURPOSE: To make a fuel injection nozzle attachable to a cylinder head and vice versa even if an oil seal is removed from the cylinder head.

CONSTITUTION: An oil seal 4 sealing an interval between a connecting part, by a nut 6, between a fuel injection nozzle 2, whose upper end is situated in an interspace surrounded by a cylinder head 1 and a cylinder head cover 7, and a fuel feeding pipe 5, and this cylinder head 1 is provided with an intermediate part 4c made to be flexible in an oil seal axial direction. At the time of attaching the fuel injection nozzle 2 and vice versa, a fuel injection nozzle side end of the oil seal 4 is shiftable in a direction separate from the fuel injection nozzle 2, so that this nozzle 2 is attachable to the cylinder head and vice versa without removing the oil seal 4 from this cylinder head 1.