To reduce the overall height of a cylinder head, reduce surfaces to be machined for supporting an intake camshaft, an exhaust cam shaft and an eccentric camshaft, reduce the number of machining directions of fastening screws, and reduce manufacturing cost by simplifying assembling steps as well as reducing the number of parts.

In this valve system apparatus for a four-stroke internal combustion engine having the intake camshaft and the exhaust camshaft, and continuously varying a lift of the intake valve by controlling rotations of the intake camshaft and the eccentric camshaft via an intermediate lever contacting the intake camshaft and the eccentric camshaft, and via a rocker arm contacting the intermediate lever, two or three between a parting surface of a bearing of the eccentric camshaft, a parting surface of a bearing of the intake camshaft, and a parting surface of a bearing of the exhaust camshaft are arranged on a coplanar surface.