Abstract: An engine fuel essentially consisting of alcohol may contain a relatively large amount of water in comparison with conventional gasoline and diesel oil, so that when water possibly penetrates into a clearance between an intake valve seat and a mounting reception portion of a cylinder head where the valve seat is to be mounted when the engine fuel essentially consisting of alcohol together with air is introduced into a cylinder through an air inlet having the intake valve seat. As a plating layer 14 is formed on the surface of an iron-based valve seat main body 17 provided at a mounting reception portion 13 formed at an air inlet 6 of a cylinder head 2 made of an aluminum alloy, the plating layer 14 intervenes between the cylinder head 2 and the valve seat main body 17, so that a potential difference between the dissimilar metals for the mounting reception portion 13 and the valve seat main body 17 is reduced through water, thereby preventing galvanic corrosion.