The present disclosure provides a flow rate measuring device for measuring a flow rate of a main flow flowing through a duct. The flow rate measuring device includes a bypass passage, a blow rate sensor, and a measurement body. The measurement body includes a measurement flow inlet and a cylindrical portion. The measurement flow inlet is open toward an upstream side of the duct. The measurement flow outlet is open toward a downstream side of the duct. The cylindrical portion is disposed to cover the measurement flow outlet. The cylindrical portion includes an outer circumferential surface, which guides the main flow, and an inner circumferential surface, which guides the measurement flow. The cylindrical portion includes a waveform portion that is formed in an edge side of an opening of the cylindrical. The waveform portion has a shape that divides the main flow guided by the cylindrical portion into a plurality of main flows and that divides the measurement flow guided by the cylindrical portion into a plurality of measurement flows.