An air intake device of an internal combustion engine having an intake passage comprises a tank which extends along the intake passage. A first pipe interconnects the tank with the intake passage and a valve disposed therein is actuated in response to the engine speed for improving the engine performance. A narrow second pipe also interconnects the tank with the intake passage and constitutes a resonator in conjunction with the tank. The second pipe opens into the intake passage upstream of a throttle valve and preferably close to an air cleaner mounted on the upstream end of the intake passage.