To provide an air-cooled internal combustion engine which has a cylinder head body having a cooling air passage with sufficient sectional area and suitably molded by die-casting.

The air-cooled internal combustion engine includes a cylinder head body 100 having: a plurality of cooling fins 10, a cam chamber wall 20 defining a cam chamber 109; a combustion chamber wall 30 defining a combustion chamber 110; an intake passage 40 for sucking air to the combustion chamber 110; an exhaust passage 50 for exhausting the combustion chamber 110; and a cooling air passage 60 for sending cooling air to between the cam chamber wall 20 and combustion chamber wall 30. The cylinder head body 100 is molded integrally from aluminum alloy by die-casting. The cylinder head body 100 further has a cam chain chamber 70 for housing a cam chain 113. The exhaust passage 50 is formed in such a way that the exhaust passage extends so as to be away from the cam chain chamber 70 as the exhaust passage 50 comes close to an exit side from an entrance side when viewed from a cylinder axis direction D1 and an axis 50x of the exhaust passage 50 is linear.