Abstract: The invention discloses a device for measuring thermal power without using movable and wearable elements, which is also appropriate for small flow of thermal power. The device measures the thermal power by means of temperature differences only and is applicable for use with various media. It is constructed so that little of the measuring thermal power is exchanged between two lines, for which reason a temperature gradient is created in the defined cross-section of the body of the measuring device. This temperature gradient is sensed by one or several pairs of sensors, the sensors of a pair always being spaced apart. Due to the exchanged measuring thermal power there appears a temperature difference in the medium being measured between the inlet and the outlet of the same line through the measuring device. This temperature difference is sensed by one or several pairs of sensors.