1. A quantification method of functional groups in an organic thin layer comprising: 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 medium energy ion scattering (MEIS) spectroscopy; carrying out spectrometry for the same reference organic thin layer as in said measuring the absolute quantity per unit area, and thereby obtaining peak intensities of the functional groups in the reference organic thin layer; carrying out the same spectrometry as in said carrying out the spectrometry for an organic thin layer to be analyzed having the same functional groups as those included in the analysis reference material of said measuring the absolute quantity per unit area, and thereby measuring peak intensities of the functional groups with unknown quantity; and comparing the peak intensities of the functional groups measured in said carrying out the spectrometry with respect to the absolute quantity of the analysis reference material in said measuring the absolute quantity per unit area, and thereby determining the absolute quantity per unit area of the functional groups with unknown quantity in the organic thin layer to be analyzed measured in said measuring the peak intensities of the functional groups.