An arrangement of a mass intake air flow measurement device suitable for integrating a humidity sensing device as well as a temperature sensing device and a pressure sensing device is provided. A second bypass passage 501 bypassing a bypass passage 205 is formed and a humidity sensing device 500 is mounted in the second bypass passage 501. A second bypass passage inlet 502 and a second bypass passage outlet 503 formed in a wall surface of the bypass passage 205 are opened parallel to the direction of flow of air flowing in the bypass passage 205.