A gas analyzer using a quadrupole mass spectrography etc. is provided with an ionization part (211) which ionizes a gas sample, a first ion detection part (212) and a second ion detection part (213) which are so provided across the ionization part (211) as to differentiate distances between each of them and the ionization part (211) from each other and which detect ions from the ionization part (211), a filter part (214) provided between the ionization part (211) and the first ion detection part (212) to selectively filter the ions from the ionization part (211), and an arithmetic unit (3) which corrects a partial pressure (PP<SUB>1</SUB>) of a specific component obtained by the first ion detection part (212) and selected by the filter part (214) with the use of a first total pressure (TP<SUB>1</SUB>) of the gas sample obtained by the first ion detection part (212) and a second total pressure (TP<SUB>2</SUB>) of the gas sample obtained by the second ion detection part (213). The gas analyzer can correct the partial pressure even in an area in which a measured value no longer follows the change of the atmospheric pressure while keeping resolution.
