An environment sensor arranged in a measuring chamber disposed in a circuit board receiving portion does not affect a flow of air through a bypass passage, and thus does not affect detection accuracy of a flow rate detection element arranged in the bypass passage. A recessed portion is disposed in a side surface of a base parallel to a flow direction A of intake air passing through a main passage and a communication port of the measuring chamber is disposed in the recessed portion, and thus the measuring chamber is unlikely to be infiltrated by fouling substances, water droplets, and the like contained in the intake air. The communication port has a small length dimension L, and thus an environment parameter of the intake air is likely to propagate to the measuring chamber and high levels of detection response, detection accuracy, and reliability are ensured for the environment sensor.