PROBLEM TO BE SOLVED: To provide a method and an apparatus that can perform easy calibration even if there is no reference substance for a measuring object at a measurement site when the apparatus is to be used.SOLUTION: A calibration method of a chemical analyzing apparatus includes steps of: connecting a reference apparatus 10 to a detector 20 replaceable with a chemical analyzing apparatus 30 for measuring the concentration of a measurement target substance in gas or liquid; bringing the detector in contact with reference object substances in gas or liquid, in which a plurality of concentrations are determined in advance; obtaining a reference analytical curve from detection values of the reference object substances and concentration values of the reference object substances, and acquiring reference gradient coefficient of the reference analytical curve per unit concentration; calculating correction coefficient for correcting the reference gradient coefficient to be equal to theoretical gradient coefficien
