PURPOSE: To heighten productivity by forming a housing, fitted at a cylinder head, of the injection body of an air fuel injection device into two-piece structure divided into an inner and an outer housings fitted coaxially, and forming a first passage at the inner housing and a second passage at the boundary part of both housings.

CONSTITUTION: An air-fuel injection device 19 mounted at the upper part of a combustion chamber 17 formed at the lower face of a cylinder head 4 is formed of an injection body 20 as a main part, a valve mechanism for switching the nozzles 26c, 26g of an air chamber and a fuel chamber as chambers formed in the injection body 20, and a fuel injection valve 22 mounted at the rear side part of the outer wall of the injection body 20. In this case, a housing 23, fitted into the fitting hole 4b of the cylinder head 4, of the injection body 20 is formed into two-piece structure divided into an outer and an inner housings 25, 26. An air passage 27 as a first passage is formed in the inner housing 26 and a fuel passage as a second passage is formed at the boundary part of both housings 25, 26.