In a variable valve opening property internal combustion engine, a roller link (22) is provided with a cam roller (31) at a free end thereof which engages a cam (3) of a camshaft (4) and a pressure surface (47) of a spring device (41). The roller link is pivotally supported by a bearing portion of a control link (21) which can be adjusted in position by using an actuator (14). The roller link is additionally provided with a roller shaft (31) that engages a slipper surface of a rocker arm (6). The pressure surface of the spring device may be contoured or otherwise inclined so that the direction of action of the spring device on the cam roller can be directed in an optimum direction irrespective of the adjusted position of the pivot point of the roller link.