Airflow measuring device

An airflow measuring device comprising:

• a case protruded in a duct and configured to receive a part of air flowing through the duct;
• a sensor accommodated in the case, the sensor being configured to conduct heat transfer with air received in the case and to send an electric signal according to a flow amount of air in the duct, wherein
• the case has
• a first passage configured to receive air from the duct and to exhaust air into the duct, and
• a second passage branched from the first passage, the second passage configured to receive air from the first passage and to exhaust air into the duct separately from the first passage, the second passage accommodating the sensor,
• the first passage has a throttle at a downstream of a branch position where the second passage is branched from the first passage, the first passage is configured to exhaust air into the duct while throttling air at the throttle,
• the throttle has a throttle wall surface having a normal vector directed toward an inside of the throttle,
• the case has a reference cross section including the branch position, the reference cross section being perpendicular to a passage axis of the duct,
• the case is configured to move air along a flow-direction vector into the second passage at the branch position,
• the reference cross section includes a reference vector, which is formed by vertically projecting the flow-direction vector on the reference cross section,
• a width direction is perpendicular to both a flow direction of air in the throttle and the reference vector, and
• the throttle wall surface has a specific region, in which
• the normal vector includes a vector component in the width direction, and
• an angle θ between the normal vector and the reference vector is in a range of 90 degrees<θ<180 degrees.