To provide an intake air flow rate measuring device capable of measuring flow rate of intake air using an air flow sensor and improving correction precision for offsetting changes of output characteristics due to aging.

When a condition in which a change rate Ne of rotational speed of an engine is within a first predetermined scope and a change rate ΔQ of engine load is within a second predetermined scope continues for predetermined hours, it is determined that the engine is in a steady operation condition (S11 to S13), and flow rate Ge of intake air corresponding to actual operation condition of the engine is inferred and computed by referring to a map for realizing performance characteristics of a turbocharger (S14 to S16). After compensating the flow rate Ge of intake air by corresponding to pressure pi and temperature Ti of intake air (S17), a compensation value C for compensating flow rate Ga of intake air is adequately renewed if an absolute value of difference between the flow rate Ga of intake air detected by the air flow sensor and the flow rate Ge of intake air inferred and computed is above a predetermined value α or more (S18 and S19).