A four cycle, 12-cylinder engine includes four cylinder (1) groups each having three cylinders located adjacent to each other. The cylinders in each cylinder group have intake strokes which are apart one from another by 240° in terms of angle of rotation of the engine crankshaft. The cylinders in each cylinder group are connected through respective branch intake passages (9) with a common intake passage (7a,b,c,d). Means (8) is provided for separating the common intake passage of one cylinder group from the common intake passage of another cylinder group.