A gas concentration detecting apparatus comprises a gas concentration sensor
and
a gas concentration calculator. The sensor has first to third cells. A gas to be
detected is introduced in a chamber and the first cell is responsible for discharging
and changing oxygen from and into the chamber. The second cell detects a concentration
of a specific gas component of the gas that has passed along the first cell. The
third cell detects a concentration of residual oxygen in the gas that remains after
discharge of the oxygen through the first cell. The calculator takes in a current
acquired from the second cell measured with a voltage applied thereto and calculates
the specific gas component concentration based on the current. The calculator includes
plural concentration calculating means whose concentration detecting ranges are
mutually different in a scale. The specific gas component concentration is calculated
every concentration calculating means.
