Abstract: A device for measuring the velocity of flow of a fluid, with at least one thermocouple (10), whose junction point is arranged in the fluid, with an a.c. power source (11) heating the thermocouple to a working temperature higher than the temperature of the fluid and with an evaluating circuit (12, 13) processing the thermocouple voltage, is to be improved such that the temperature dependence of the heat conductivity of the fluid to be investigated is compensated in a simple manner. To accomplish this object, the temperature coefficient of the ohmic resistance of the thermocouple (10) is adapted to the temperature dependence of the heat conductivity of the fluid such that the heating power converted in the thermocouple (10) during a change in temperature and unchanged current varies by exactly the same amount as the amount of heat released to the fluid due to the changed heat conduction.