Abstract: This invention provides a heater controller applied to an air-fuel ratio sensor to prevent the sensor being cooled after a return from a fuel-cut state.The temperature of a detecting element 111 of an air-fuel ratio sensor 11 is maintained at a fixed temperature by beating the heater 112, and an electric power supplied to the heater is controlled by controlling a switching element 122 of a driving circuit 12 to a proper duty ratio. The sensor is cooled during the fuel-cut state because intake air is directly exhausted to an exhaust pipe, and the temperature of the sensor does not return to the proper temperature after a return from the fuel-cut state because the ambient temperature does not immediately return to the temperature before the fuel-cut state. Therefore a heater controller prevents the sensor being cooled by increasing an electric power after the return from the fuel-cut state in accordance with an integrated intake air-flow rate during the fuel-cut state.