Abstract: A valve actuating mechanism is disposed within a four-stroke cycle engine and comprises a rotatable rocker shaft having eccentric large-diameter portions formed as bushings upon the rocker shaft, a rocker arm assembly including a first rocker arm rotatably mounted directly upon the rocker shaft and second and third rocker arms rotatably muonted upon the eccentric bushings of the rocker shaft with the first rocker arm being interposed between the second and third rocker arms, and a cam assembly including first, second and third cam members which drives the first, second and third rocker arms, respectively. The first rocker arm is provided with a branched distal end and the second and third rocker arms are each provided with a distal end which is laid upon each of the distal ends of the first rocker arm. The second and third cams have the same cam profile and the first cam has a cam profile which is different from that of the second and third cams.