PURPOSE: To make it possible to accurately detect a wide range of a flow amount with high sensitivity, by fixing not only a resistance heat generator to the single surface of an insulating substrate but also two temp.-sensitive resistors to the other surface thereof to constitute a detection part and arranging the surface of said detection part along the direction of a gas stream to be detected while supplying the resistance heat generator to heat the same.

CONSTITUTION: The surfaces of the temp.-sensitive resistors 2, 3 of a detection part S are allowed to coincide with the direction of the stream of gas, for example, air of which the flow amount must be detected and the detection part S is earthed. The air stream being the gas stream changes not only the temp. distribution of a substrate 1 heated by a resistance heat generator 4 generating heat by the current applied from a power source 7 but also the resistance value ratio of the resistors 2, 3 fixed to the substrate 1. As a result, the signal voltage corresponding to the flow speed or flow amount of the air stream is generated between output terminals 10, 11. Because the flow amount of this gas is the function of the product of the cross-sectional area and flow speed of the flowing gas, if signal voltage is measured, the flow amount can be determined.