A crystalline phase identification method for identifying a crystalline phase contained in a sample, wherein the crystalline phase contained in the sample is identified from: X-ray diffraction data of the sample which contain data of a plurality of ring-shaped diffraction patterns, and a database in which are registered data related to peak positions of X-ray diffraction patterns for a plurality of crystalline phases and data related to peak intensity ratios of X-ray diffraction patterns for a plurality of crystalline phases, the crystalline phase identification method characterized in that: peak positions and peak intensities are detected for a plurality of the diffraction patterns from the X-ray diffraction data; circumferential angle (β) versus intensity data is created for the plurality of the diffraction patterns for which the peak positions and peak intensities were detected, at the detected peak positions, from the X-ray diffraction data; the diffraction patterns are grouped into a plurality of clusters on the basis of the uniformity of each of the circumferential angle (β) versus intensity data thus created (S104, S105); and a search is made for crystalline phase candidates contained in the sample from the database on the basis of sets of peak positions and peak intensity ratios of the diffraction patterns grouped into the same cluster. wherein the crystalline phase contained in the sample is identified from: X-ray diffraction data of the sample which contain data of a plurality of ring-shaped diffraction patterns, and a database in which are registered data related to peak positions of X-ray diffraction patterns for a plurality of crystalline phases and data related to peak intensity ratios of X-ray diffraction patterns for a plurality of crystalline phases, X-ray diffraction data of the sample which contain data of a plurality of ring-shaped diffraction patterns, and a database in which are registered data related to peak positions of X-ray diffraction patterns for a plurality of crystalline phases and data related to peak intensity ratios of X-ray diffraction patterns for a plurality of crystalline phases, the crystalline phase identification method characterized in that: peak positions and peak intensities are detected for a plurality of the diffraction patterns from the X-ray diffraction data; circumferential angle (β) versus intensity data is created for the plurality of the diffraction patterns for which the peak positions and peak intensities were detected, at the detected peak positions, from the X-ray diffraction data; the diffraction patterns are grouped into a plurality of clusters on the basis of the uniformity of each of the circumferential angle (β) versus intensity data thus created (S104, S105); and a search is made for crystalline phase candidates contained in the sample from the database on the basis of sets of peak positions and peak intensity ratios of the diffraction patterns grouped into the same cluster. peak positions and peak intensities are detected for a plurality of the diffraction patterns from the X-ray diffraction data; circumferential angle (β) versus intensity data is created for the plurality of the diffraction patterns for which the peak positions and peak intensities were detected, at the detected peak positions, from the X-ray diffraction data; the diffraction patterns are grouped into a plurality of clusters on the basis of the uniformity of each of the circumferential angle (β) versus intensity data thus created (S104, S105); and a search is made for crystalline phase candidates contained in the sample from the database on the basis of sets of peak positions and peak intensity ratios of the diffraction patterns grouped into the same cluster.