An air flow rate measurement device capable of suppressing disturbance of a flow of measured gas and reducing a characteristic influence due to water droplets flowing with intake air is realized. An edge 800 of the upstream side where air flows in a circuit board 400 on which a flow rate detection portion 602 is mounted is provided with a segmentation portion 801 to be a semicircular notch structure to segment the edge 800. Water droplets flowing with measured gas 30 can be captured by the segmentation portion 801 to inhibit the water droplets from arriving at the flow rate detection portion 602.