To ensure highly accurate response lag compensation regardless of the velocity of air flow, when the air flow rate is detected through heating elements arranged in an air channel, by providing a response compensation circuit being controlled to have a response time constant corresponding to the velocity of air flow.

The air flow rate measuring unit being employed for engine control of an automobile, or the like, comprises a circuit 2 for compensating the response lag of a signal corresponding to the velocity of air flow detected through a Wheatstone bridge circuit comprising a heating element 11 and a temperature compensation resistor 12. The compensation circuit 2 comprises a phase lead circuit employing a control resistor having resistance variable through a control voltage and an appropriate time constant corresponding to the velocity of air flow can be attained by controlling the control voltage appropriately with reference to a signal corresponding to the air flow rate. The control resistor comprises a plurality of field effect transistor, i.e., switching elements, connected in parallel and the combined resistance is determined by the voltage of the reference signal.