Intake camshafts 10, 14 for driving valve bodies 32 (intake valve) are positioned in right- and left-hand banks, respectively. A variable valve mechanism 30 is positioned in each of the right- and left-hand banks in such a manner as to form mirror-image symmetry. The variable valve mechanism 30 includes a control shaft 60 for controlling the operating angle of the valve body. The respective control shafts in the right- and left-hand banks are controlled in symmetrical directions. The right- and left-hand intake camshafts 10, 14 rotate in opposite directions and at a speed that is synchronized with the speed of a crankshaft.