An engine which is a single cylinder engine comprising: a cylinder body; a cylinder head including a combustion chamber and a cam chain chamber arranged in a direction which is orthogonal to a cylinder axis of the cylinder body with regard to the combustion chamber, the cylinder head being attached to the cylinder body; a head cover including an end section arranged to face an end section of the cylinder head, the head cover being attached to the cylinder head; a cam chain arranged in the cam chain chamber; a cam shaft linked with the cam chain, the cam shaft being supported by the cylinder head; a rocker shaft supported by the cylinder head, the rocker shaft being parallel to the cam shaft; a first rocker arm supported by the rocker shaft; a second rocker arm supported by the rocker shaft, the second rocker arm being arranged to line up with the first rocker arm in an axial direction of the cam shaft; a switching pin member configured to be moved in the axial direction of the cam shaft, the switching pin member being configured to be moved between a first position at which the first rocker arm and the second rocker arm are linked and a second position at which the first rocker arm and the second rocker arm are not linked, the switching pin member being configured to swing together with the first rocker arm and the second rocker arm at the first position; and an actuator configured to switch the position of the switching pin member between the first position and the second position by pressurizing the switching pin member in the axial direction of the cam shaft, wherein at least a portion of the switching pin member overlaps with the head cover when viewed from the axial direction of the cam shaft, the actuator is arranged on the opposite side to the cam chain chamber with regard to the cam shaft in the axial direction of the cam shaft, and the actuator is arranged outside of the engine, characterized in that the actuator is positioned more to the head cover side than the end section of the cylinder head. a cylinder body; a cylinder head including a combustion chamber and a cam chain chamber arranged in a direction which is orthogonal to a cylinder axis of the cylinder body with regard to the combustion chamber, the cylinder head being attached to the cylinder body; a head cover including an end section arranged to face an end section of the cylinder head, the head cover being attached to the cylinder head; a cam chain arranged in the cam chain chamber; a cam shaft linked with the cam chain, the cam shaft being supported by the cylinder head; a rocker shaft supported by the cylinder head, the rocker shaft being parallel to the cam shaft; a first rocker arm supported by the rocker shaft; a second rocker arm supported by the rocker shaft, the second rocker arm being arranged to line up with the first rocker arm in an axial direction of the cam shaft; a switching pin member configured to be moved in the axial direction of the cam shaft, the switching pin member being configured to be moved between a first position at which the first rocker arm and the second rocker arm are linked and a second position at which the first rocker arm and the second rocker arm are not linked, the switching pin member being configured to swing together with the first rocker arm and the second rocker arm at the first position; and an actuator configured to switch the position of the switching pin member between the first position and the second position by pressurizing the switching pin member in the axial direction of the cam shaft,