An air flow rate measurement device includes a casing, a flow rate measurement portion, a first protrusion and a second protrusion. The casing is disposed in a main flow passage in which an air flows, and the casing defines a bypass passage therein to take in a part of the air flowing in the main flow passage. The flow rate measurement portion is housed in the casing and measures a flow rate of the air flowing in the bypass passage. The first protrusion protrudes from a side surface of the casing in the main flow passage. The second protrusion protrudes from the side surface of the casing in the main flow passage. The second protrusion is spaced from the first protrusion in a flow direction of the air in the main flow passage. The air flow rate measurement device is capable of limiting a generation of a separated vortex.