A device for measuring the mass of a flowing medium by use of a temperature-dependent measuring resistor bathed by the flowing medium and accommodated in a measuring channel. The device has a flow obstacle, embodied in the form of a trip edge, upstream of the measuring element in the region of an inlet opening of the measuring channel, so as to create a chronologically and spatially stable separation zone in the region of the trip edge, thereby preventing chronologically and spatially unstable separation zones and makes it possible to attain a reduction in measuring signal noise. The invention is contemplated for measuring the mass of a flowing medium, especially for measuring the aspirated air mass in internal combustion engines.