th aspect of the invention, there is provided a gas concentration measuring apparatus which comprises: (a) a gas concentration sensor including a sensor element producing a gas concentration signal indicative of the concentration of a preselected component contained in gasses, a heater heating the sensor element, and an insulator disposed between the sensor element and the heater; (b) a heater control circuit supplying power to the heater cyclically using a pulse-width modulated (PWM) signal; and (c) a correction circuit 