A mass spectrometry method includes: preparing calibration data for performing calibration on a basis of first data obtained by detecting a chlorobiphenyl in first mass spectrometry of a reference sample of the chlorobiphenyl; acquiring second data obtained by detecting, in second mass spectrometry of a sample, at least one chlorobiphenyl that has a same chlorine number as and is different in kind from the chlorobiphenyl detected in the first mass spectrometry; and calculating a quantitative value for the chlorobiphenyl contained in the sample on a basis of the calibration data and the second data.