1. A pattern discriminating apparatus comprising: a setting unit configured to set at least one three-dimensional area in a three-dimensional space in a three-dimensional image data; a feature value calculating unit configured to calculate a pixel feature value from one pixel to another of the three-dimensional image data; a matrix calculating unit configured to (1) calculate plural mapping points on a three-dimensional coordinate in the area which are displaced in position in respective three-dimensional directions from a focused point on the three-dimensional coordinate in the area by a mapping with plural three-dimensional displacement vectors, and (2) calculate a co-occurrence matrix which expresses the frequency of occurrence of a combination of the pixel feature value of the focused point in the area and the pixel feature values of the mapping points in the respective three-dimensional directions for each of the displacement vectors; and a discriminating unit configured to calculate a value for discrimination from a vector which is learned and a constant term which is learned from a learning sample of an object to be detected, and the co-occurrence matrix for each of the three-dimensional displacement vectors, compare the value for discrimination and a threshold value with each other, and thereby discriminate whether or not the object to be detected is imaged in the three-dimensional area.