Each cylinder is provided with a first intake valve and a second intake valve, and a first intake cam for driving the first intake valve and a second intake cam for driving the second intake valve are coaxially pivotally supported on an intake camshaft. A first cam phase change mechanism which varies respective phases of the first and second intake cams relative to a crankshaft of the internal combustion engine is combined with a second cam phase change mechanism which varies a phase of the second intake cam relative to the first intake cam. The second cam phase change mechanism is set to have a variable-phase angular range wider than that of the first cam phase change mechanism.