An air intake device of an engine has intake pipes connected to each of the engine cylinders divided into first and second groups to prevent the continuance of the intake strokes of adjacent cylinders. A first connecting cavity connected to the first group of cylinders and a second connecting cavity connected to the second group of cylinders are arranged in parallel with each other, for effecting supercharging by utilizing the dynamic effect of intake air into each cylinder. A first communicating passage is connected at one end to a longitudinal end of the first connecting cavity and at the other end to a longitudinal end of the second connecting cavity. A second communicating passage arranged on the same side as the first communicating passage is connected at one end to a side of the first connecting cavity and at the other end to a side of the second collecting cavity. The effective passage length of the first communicating passage is shorter than that of the second communicating passage.