INTERNAL COMBUSTION ENGINE

A valve seat 30 has a port connection surface 32 which connects between a downstream intake port surface 24 and a valve resting surface 31 and intersects with the downstream intake port surface 24. The valve seat 30 has an edge 33 which is defined by a line-shaped sharp corner lying on an intersection between the downstream intake port surface 24 and the port connection surface 32. Recesses 25A, 25B, and 25C are formed to extend in a direction in which the intake port 23 extends. The recesses 25A, 25B, and 25C are hollowed in the downstream intake port surface 24 and the port connection surface 32 to increase a transverse sectional area thereof. The recesses 25A, 25B, and 25C are arranged adjacent each other in a circumferential direction of the intake port 23. These arrangements ensure the stability in creating a tumble flow 40 of intake air in a combustion chamber 5 and enhances the efficiency in supplying the intake air into the combustion chamber 5.