An airflow measuring device includes a sensing portion provided in a bypass passage, which perpendicularly deflects part of air from a main passage to therethrough bypass the part of air. The sensing portion includes a heating resistor energized and dissipate heat to airflow. The sensing portion is configured to measure airflow in the bypass passage based on the heat radiation. The sensing portion further includes a pair of support members erected in the bypass passage to support the heating resistor. The heating resistor of the sensing portion is inclined at a first inclination angle with respect to a direction, which is perpendicular to a flow direction of air in the bypass passage. The heating resistor is inclined toward downstream at an outer streamline of the airflow in the bypass passage.