An intake air flow rate detection device for an internal combustion engine, the engine comprising an intake passage through which intake air flows, a supercharging device that supercharges the intake air, a throttle that throttles the intake air downstream of the supercharging device, a bypass passage that bifurcates between the supercharging device and the throttle and converges with the intake passage upstream of the supercharging device, and a bypass valve that opens and closes the bypass passage, the detection device comprising: a sensor (61, 63) that detects an operating condition of the internal combustion engine; an air flow meter that disposed in the intake passage upstream of the supercharging device; and a programmable controller programmed to: calculate a measured intake air flow rate from a detection value of the air flow meter; calculate a calculated intake air flow rate from the operating condition of the internal combustion engine; and employ either the measured intake air flow rate or the calculated intake air flow rate as an intake air flow rate of the intake passage on the basis of a circulated air flow rate that is a flow rate of air circulated to the intake passage between the air flow meter and the supercharging device through the bypass passage, characterized in that the controller is further programmed to: calculate an opening of the bypass valve; set an opening reference value (D 0) above which the circulated air is determined to flow back to the air flow meter, the opening reference value (D 0) having a characteristic to increase as an engine rotation speed increases; employ the measured intake air flow rate when the calculated opening is not greater than the opening reference value (D 0); and employ the calculated intake air flow rate when the calculated opening is greater than the opening reference value (D 0). a sensor (61, 63) that detects an operating condition of the internal combustion engine; an air flow meter that disposed in the intake passage upstream of the supercharging device; and a programmable controller programmed to: calculate a measured intake air flow rate from a detection value of the air flow meter; calculate a calculated intake air flow rate from the operating condition of the internal combustion engine; and employ either the measured intake air flow rate or the calculated intake air flow rate as an intake air flow rate of the intake passage on the basis of a circulated air flow rate that is a flow rate of air circulated to the intake passage between the air flow meter and the supercharging device through the bypass passage, characterized in that the controller is further programmed to: calculate an opening of the bypass valve; set an opening reference value (D 0) above which the circulated air is determined to flow back to the air flow meter, the opening reference value (D 0) having a characteristic to increase as an engine rotation speed increases; employ the measured intake air flow rate when the calculated opening is not greater than the opening reference value (D 0); and employ the calculated intake air flow rate when the calculated opening is greater than the opening reference value (D 0). calculate a measured intake air flow rate from a detection value of the air flow meter; calculate a calculated intake air flow rate from the operating condition of the internal combustion engine; and employ either the measured intake air flow rate or the calculated intake air flow rate as an intake air flow rate of the intake passage on the basis of a circulated air flow rate that is a flow rate of air circulated to the intake passage between the air flow meter and the supercharging device through the bypass passage, characterized in that the controller is further programmed to: calculate an opening of the bypass valve; set an opening reference value (D 0) above which the circulated air is determined to flow back to the air flow meter, the opening reference value (D 0) having a characteristic to increase as an engine rotation speed increases; employ the measured intake air flow rate when the calculated opening is not greater than the opening reference value (D 0); and employ the calculated intake air flow rate when the calculated opening is greater than the opening reference value (D 0). calculate an opening of the bypass valve; set an opening reference value (D 0) above which the circulated air is determined to flow back to the air flow meter, the opening reference value (D 0) having a characteristic to increase as an engine rotation speed increases; employ the measured intake air flow rate when the calculated opening is not greater than the opening reference value (D 0); and employ the calculated intake air flow rate when the calculated opening is greater than the opening reference value (D 0).