PURPOSE: To prevent the corrosion, deterioration and wire snapping or the like of the metal parts of electric system members by providing a cut off space at a place adjacent to a combustion chamber or an air intake passage, and housing fuel injector electric system members into the space.

CONSTITUTION: A fitting portion 25 to fit an injector 24 is formed in adjacency of an air intake passage 30 communicating respectively with the air intake passages 5 of an engine body 1. The fitting portion 25 is separated from the air intake passage 30 by means of a partition wall 17 except for an opening 29 whose purpose is to insert the tip of the injector 24 into the air intake passage 30. The air intake passage 30 and a space 18 at the perimeter of the injector 24 surrounded with the partition wall 17, are cut off air-tightly by inserting the injector 24 into the opening 29 through a rubber ring 28. At the space 18, an electrical wiring connector 20, a lead wire 44, an intaken air temperature sensor 46, and its electric wiring connector 48 or the like, in addition to the injector 24, are housed, and they are protected well from water, salinity or the like in atmosphere or air intaken.