To provide a flow detecting mechanism capable of more facilitating manufacture, reducing the cost and size to a compact, hardly causing variation in the individual assembled states, and improving measurement accuracy.

In this flow detecting mechanism, a fluid F is divided into a sensor passage 1 and a by-pass passage 2, and according to the flow dividing ratio of the fluid F and the flow detecting information on the fluid F flowing through the sensor passage 1, the total quantity of the introduced fluid is detected. A resisting material 6 inserted in the by-pass passage 2 is formed by stacking plural etching plates 8 by a soldering junction, or diffused junction.