An air intake structure of an engine has a first intake air passage and a second intake air passage provided independently and having downstream end portions branched into a plurality of intake ducts connected to a plurality of cylinders of the engine. The neighborhood of the downstream end portion of the first intake air passage and the neighborhood of the down stream end portion of the second intake air passage can be brought into communication by a first communication element. The first intake air passage and the second intake air passage are rendered communicable by a second communication element upstream from the first communication element in the flowing direction of intake air. The first communication element and the second communication element are controlled in accordance with the operating state of the engine.