Valve operating system in internal combustion engine

In a valve operating system in an internal combustion engine, the operational characteristic of an engine valve which is an intake valve or an exhaust valve can be changed in accordance with the operational state of the engine, the reduction in size thereof can achieved and moreover, the operational characteristic of the engine valve can be finely changed, and the lifted state of the engine valve can be detected simply. A power transmitting device is formed of an inner wheel, an outer wheel and a carrier which rotatably carries a planetary rotor. Among these components forming the power transmitting device, a first component is operatively connected to a cam shaft, and a second component is connected to an engine valve. A rotational amount control device connected to a third component, controls the amount of rotation of the third component in accordance with the operational state of the engine. A first discharge bore is provided in a support shaft supporting the inner wheel and leads to an oil passage, and a second discharge bore provided in the inner wheel, communicates with the first discharge bore. The area of communication of the second discharge bore with the first discharge bore can be changed with a change in the amount of relative angular displacement of the inner wheel relative to the support shaft.