To improve engine characteristics, fuel consumption efficiency, durability, a high rotational follow-up property, etc.

This valve system of the 4-cycle engine is provided with a fulcrum member 28 to rotate around a fulcrum revolution shaft 29, and a first actuator 32 to rotate this fulcrum member 28. A tip of the fulcrum member 28 is arranged between a force point and a working point of the rocker arm to make a fulcrum of the rocker arm 26. A valve lift quantity of the suction valve 11 is varied by rotating the supporting member 28. Further, two suction cams 17, 18 having different cam profiles for each of cylinders are provided, and two pressure rollers 58, 59 corresponding to the cylinders are also provided. One of the rollers is selectively inserted between one of the two suction cams 17, 18 and the force point of the rocker arm 26 by a second actuator 62. By this arrangement, the rocker arm 26 is driven along a cam profile of only a selected suction cum to lift the suction valve 11.