Abstract: The invention relates to a device for measuring the flow rate Q of a fluid in a fluid passage, in a well, the device comprising a first venturi section and first means responsive to the pressure difference .DELTA.P.sub.1 across the first venturi section between two points that are separate from each other in the flow direction. It comprises a second venturi section, and second means responsive to the pressure difference .DELTA.P.sub.2 across the second venturi section between two points that are separate in the flow direction, the two venturi sections being disposed relative to each other in such a manner that for a given direction of fluid flow, the diameter of one of them increases whereas the diameter to the other one of them decreases, said venturi sections being further arranged in such a way that the static pressure components present in said pressure differences .DELTA.P.sub.1 and .DELTA.P.sub.2 can be cancelled out.