An internal combustion engine comprising: a cylinder head provided with an intake opening portion connected to a combustion chamber and an intake port connected to the intake opening portion ; an annular valve seat provided with a circular seating portion and a circular outer peripheral surface and installed on a combustion chamber side of the intake opening portion ; and an intake valve seated on the seating portion when the intake valve is closed, wherein: the valve seat is provided with a port surface and a seat surface having end portions in contact with each other on an outer peripheral side of the combustion chamber along a linear edge portion ; the port surface is continuously connected to a wall surface of the intake port and the port surface has a normal vector having a direction away from the combustion chamber ; the seat surface is formed to include the seating portion and the seat surface has a normal vector having a direction approaching the combustion chamber ; a center of the outer peripheral surface of the valve seat is offset from a center of the seating portion to the port surface side; and characterized in that : the port surface includes a planar portion with no curvature; and the edge portion includes an end portion of the planar portion . a cylinder head provided with an intake opening portion connected to a combustion chamber and an intake port connected to the intake opening portion ; an annular valve seat provided with a circular seating portion and a circular outer peripheral surface and installed on a combustion chamber side of the intake opening portion ; and an intake valve seated on the seating portion when the intake valve is closed, wherein: the valve seat is provided with a port surface and a seat surface having end portions in contact with each other on an outer peripheral side of the combustion chamber along a linear edge portion ; the port surface is continuously connected to a wall surface of the intake port and the port surface has a normal vector having a direction away from the combustion chamber ; the seat surface is formed to include the seating portion and the seat surface has a normal vector having a direction approaching the combustion chamber ; a center of the outer peripheral surface of the valve seat is offset from a center of the seating portion to the port surface side; and the valve seat is provided with a port surface and a seat surface having end portions in contact with each other on an outer peripheral side of the combustion chamber along a linear edge portion ; the port surface is continuously connected to a wall surface of the intake port and the port surface has a normal vector having a direction away from the combustion chamber ; the seat surface is formed to include the seating portion and the seat surface has a normal vector having a direction approaching the combustion chamber ; a center of the outer peripheral surface of the valve seat is offset from a center of the seating portion to the port surface side; and characterized in that : the port surface includes a planar portion with no curvature; and the edge portion includes an end portion of the planar portion . the port surface includes a planar portion with no curvature; and the edge portion includes an end portion of the planar portion . <EOS>