A quantification method of functional groups in an organic thin layer includes: a) measuring an absolute quantity per unit area of an analysis reference material having functional groups included in a reference organic thin layer by means of MEIS spectroscopy; b) carrying out spectrometry for the same reference organic thin layer as in a) and thereby obtaining peak intensities of the functional groups in the reference organic thin layer; c) carrying out the same spectrometry as in b) for an organic thin layer to be analyzed having the same functional groups and thereby measuring peak intensities of the functional groups with unknown quantity; and d) comparing the peak intensities of the functional groups measured in b) with respect to the absolute quantity of the analysis reference material in a) and thereby determining the absolute quantity per unit area of the functional groups with unknown quantity measured in c).