1. An analyzer of bone mineral density using CT image data, created from a CT scanner, of a phantom having a known bone mineral density, the analyzer comprising: a known data storage part that stores known data of bone mineral density for a phantom; a processor configured to perform on or more of: a histogram production that produces a histogram of region number relative to a CT value for three-dimensional CT image data of the phantom; a correspondence determination that receives said histogram from said histogram production and determines correspondence between a CT value and a bone mineral density by correlating CT values showing respective peaks of the produced histogram with the known data of the phantom; and an analysis that receives the correspondence between the CT value and bone density determined by the correspondence determination and decides a bone mineral density for three-dimensional CT image data of a subject using the determined correspondence and outputs said determined bone mineral density, wherein the correspondence determination discriminates that, when a peak is included in a range of a prescribed number of counts of the produced histogram, the peak is one to be correlated with the known data.