An air flow sensor for an internal combustion engine is disclosed. An air flow rate measurement meter, a pressure gauge, electronically controlled throttle body, and the microcomputer, etc. are integrated as one body, and the correction of the air flow rate, the control, and the fault diagnosis, etc. are done in the integrated microcomputer. The air flow sensor outputs an air flow rate signal in which the error is deleted to suppress the discharge of the harmful exhaust gas from the internal combustion engine, carries out the self-diagnosis of the breakdown of the air flow sensor or the electronically controlled throttle body to prevent the accident beforehand, and controls to obtain the best intake air amount.