#7 cylinder shares an exhaust manifold with #1 cylinder and is fired a predetermined firing interval after #1 cylinder. An exhaust cam shaft has a first cam for driving the exhaust cams of #1 cylinder and a second cam for driving the exhaust cams of #7 cylinder. A valve overlap period of #1 cylinder during its shift from an exhaust stroke to an intake stroke overlaps a time period during which the exhaust valves of the second cylinder are open in #7 cylinder while it is shifting from a power stroke to an exhaust stroke. The nose of the second cam is located farther in a retard direction than a position that is away in the retard direction from the nose of the first cam by an angle corresponding to the predetermined firing interval between the first and second cylinders.