A gas sensing apparatus is disclosed including a gas sensing device that is self-heated due to an applied voltage, whose resistance variation amount is varied to thereby sense gas; a voltage supply for variably supplying a voltage to the gas sensing device; a current detector for detecting the current flowing through the gas sensing device thereby generating a current-voltage characteristic for the gas sensing apparatus under the effect of a given gas exposure; and a control and judgement portion for controlling the voltage supply to control a variation value of a voltage supplied to the gas sensing device and to determine the kind and density of a gas in an ambient atmosphere, using current-voltage characteristic reference data.