The gas detecting system of the present invention is equipped with a catalytic combustion type gas sensor 1a and a semiconductor type gas sensor 1b, in a gas detecting system 1 having an operating sate in which generation of electricity is performed, and an idling state, at the time of the operating state, detection of the detection target gas is performed by the catalytic combustion type gas sensor 1a, whereas at the time of the idling state, detection of the detection target gas is performed by the semiconductor type gas sensor 1b.