An internal combustion engine includes: a head cover covering a cylinder head; and a variable valve actuation mechanism. The variable valve actuation mechanism includes: a cam placed inside the head cover and rotating with a camshaft extending in a rotation axis direction; and an intermediate arm placed inside the head cover and sandwiched between the cam and a rocker arm. A pair of side through-holes, which are provided for a support rod supporting the intermediate arm to pass through, are formed in side portions of the head cover so as to face each other along the rotation axis direction.