A concentration detector comprises oxygen-forming means for forming oxygen
by decomposing the particular component in the gas, first output means
for producing an output value proportional to the oxygen concentration in
the gas of before oxygen is formed by the oxygen-forming means, second
output means for producing an output value proportional to the oxygen
concentration in the gas after oxygen is formed by the oxygen-forming
means, concentration calculation means for calculating the concentration
of the particular component in the gas based upon the output value from
the first output means and upon the output value from the second output
means by using a coefficient for bringing the output characteristics of
the first output means into agreement with the output characteristics of
the second output means, and means which feeds at least two kinds of
gases containing the particular component at a constant concentration and
containing oxygen at different concentrations to said first output means
and calculates said coefficient based on the output value from the first
output means and on the output value from the second output means.