An airflow velocity measuring apparatus that includes a fixed-temperature heat generating device. The fixed-temperature heat generating device includes a power supply, a positive-temperature-coefficient thermistor element, a switching element, a comparator element, a first negative-temperature-coefficient thermistor element, a second negative-temperature-coefficient thermistor element, and plural resistor elements. The positive-temperature-coefficient thermistor element is disposed at a measuring point at which the velocity of airflow is measured. The switching element is repeatedly turned ON and OFF so as to cause the positive-temperature-coefficient thermistor element to generate heat at a preset temperature, thereby applying a pulse voltage from the power supply to the positive-temperature-coefficient thermistor element. The airflow velocity measuring apparatus measures the velocity of airflow at the measuring point based on the waveform of this pulse voltage. Adding of a second switch makes it possible to correct measurement errors caused by a rise or a fall in the temperature of subject airflow.