1. A chromatogram peak purity determination apparatus for use in a data processing apparatus for chromatographs, which use photodiode array detector as a detector for collecting 3-dimensional data whose dimensions consist of retention time, wavelength and absorbance, for determining the purity of a peak that exists in a chromatogram that is prepared based on said 3-dimensional data and comprising: a) an absorbance accumulation means for accumulating, at each retention time, absorbance in the wavelength direction for all or a part of a wavelength range in a predetermined retention time range; b) an equal absorbance accumulation value group extracting means for extracting a plurality of groups wherein, for each group, the absorbance accumulation value is the same for one point on a rising slope and one point on a falling slope with respect to a peak that exists on a chromatogram that is prepared based on a 2-dimensional data whose dimensions are said absorbance accumulation value and retention time; c) a similarity calculation means for calculating similarity between absorption spectrum pattern at one point on the rising slope and absorption spectrum pattern at one point on the falling slope for each group that is extracted by said equal absorbance accumulation value group extracting means; and d) a determination means for determining, with respect to the plurality of groups that are extracted by said absorbance accumulation value group extracting means, whether or not said peak consists of a single component based on similarity that is calculated by said similarity calculation means.