PURPOSE:To smooth the switching of a valve between its operating condition and its resting condition,by providing such an arrangement that a support member forming a fulcrum for a rocker arm is changed between its direct support condition and its floating condition by means of a pressing member through an intermediate member. CONSTITUTION:In an engine in which each cylinder has a low load intake port, a high load intake port and an exhaust port, a high load intake valve 5b is provided with a valve resting emchanism 19. This valve resting mechanism 19 comprises a support member 13 slidably fitted in a fitting hole 1'a in a bearing member 101 which is secured to the body of the engine, an intermediate member 16 slidably disposed in the support member 13 and urged upward by a spring 17, and pressing member 18 including a cam which is abutted against the upper surface of the intermediate member 16. When the depression of the pressing member 18 against the intermediate member 16 is released, the intermediate member 16 is separated from the support member 13 by the spring 17 so that a rocker arm 12 is set in its floating condition, thereby the intake valve 5b is rested.
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