An air flow meter (14) has a housing (21). The housing (21) comprises a measuring channel (32) which is provided with a flow rate detector, and a measuring outlet (33c) at a downstream end of the measuring channel (32). An outer peripheral surface of the housing (21) has a flat surface (44) and a curved surface (45). The flat surface (44) is provided in a depth direction Z at an intermediate position between an upstream outer peripheral end (132a) and a downstream outer peripheral end (132b), and the curved surface (45) extends from the flat surface (44) toward the upstream one Outer peripheral end (132a). A boundary between the flat surface (44) and the curved surface (45) includes a vertical boundary (131a) extending in the height direction (Y), and the measurement outlet (33c) is positioned to extend in the depth direction Z extends beyond the vertical limit (131a). Measurement accuracy of a physical quantity can be increased.
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