Cylinder head of internal combustion engine and method of producing same

A cylinder head (1) of an internal combustion engine comprises a structure cast (1) in metal, the structure defining therein an intake port (3) and having a side wall surface (5) from which an upstream end of the intake port (3) is exposed to the outside; and a partition plate (6) of metal installed in the intake port to divide the same into two parallel intake conduits (3a,3b), the partition plate having lateral edges (6a-1,6a-2) which are embedded in an inner wall of the intake port (3). The partition plate (6) has an upstream edge (6c) which includes a major straight portion (6c-1) and two projected end portions (6c-2,6c-3) which are provided on both ends of the major straight portion respectively, and the major straight portion (6c-1) is positioned inside relative to the side wall surface (5) and the two projected end portions (6c-2,6c-3) have upstream edges which are embedded in the inner wall of the intake port (3) and machined to be flush with the side wall surface (5).