Gas sensor

A gas sensor for detecting a to-be-detected gas contained in a target atmosphere, the gas sensor comprising:

• a first detection element and a second detection element connected in series to form one side of a bridge circuit,
• the first detection element being exposed to a reference atmosphere obtained by removing the to-be-detected gas from the target atmosphere and having a resistance value changing in response to own temperature change thereof,
• the second detection element being connected in series to the first detection element, exposed to the target atmosphere, and having a resistance value changing in response to own temperature change thereof;
• an amplifying circuit configured to output an amplified voltage on the basis of an intermediate voltage between the first detection element and the second detection element when a predetermined voltage is applied to the bridge circuit;
• a non-amplifying circuit configured to output the intermediate voltage as it is as a non-amplified voltage;
• and
• a control unit to which the amplified voltage and the non-amplified voltage are inputted, wherein
• the control unit calculates a concentration of the to-be-detected gas on the basis of the inputted amplified voltage, and determines presence or absence of a failure of the gas sensor on the basis of at least the non-amplified voltage.