A gas analyzer using a quadrupole mass spectrometric method etc. is provided with an ionizer to ionize a sample gas, a first ion detector and a second ion detector each configured to detect a respective ion from ionizer, and each being disposed a respective distance from the ionizer on an opposite side of the ionizer, the respective distances being different from each other, a filter interposed between the ionizer and the first ion detector to selectively allow ions from the ionizer to pass therethrough, and an arithmetic device to correct a partial pressure of a specific component obtained from the first ion detector and selected by the filter by using a first total pressure of the sample gas obtained from the first ion detector and a second total pressure of the sample gas obtained from the second ion detector.