In order to obtain a small air intake device for an internal combustion engine, which can satisfactorily control an air current and can reduce the loss of energy in a rotary valve, the air intake device is comprised of a surge tank; a first air intake path in communication with the surge tank; a second air intake path in communication with the surge tank; a casing provided with a first port connected to the first air intake path, a second port connected to the second air intake path, and an outlet port connected to an air intake portion of an internal combustion engine; a rotary valve which has a rotor contained in a valve case portion of the casing so as to rotate about the core of a rotary shaft, to control the intake air supplied to the air intake portion by the rotation of the rotor; and a first seal which seals a gap between the rotor and the portion of the valve case portion, which is opposed to the rotor, when at least any of the first port, the second port, and the outlet port is closed by the rotor.