An acting force transmission device for use with a valve mechanism of an engine includes an acting force transmission member that transmits an acting force to a valve to open/close the valve. A support shaft is provided in the acting force transmission member. An annular roller is directly mounted on an outer periphery of the support shaft. The roller is adapted to rotate when subjected to a cam force exerted by a cam and is adapted to transmit the cam force to the acting force transmission member as the acting force. A ratio d/D of an inner diameter d to an outer diameter D of the annular roller is not less than 0.7.