A graph display apparatus comprising: a display unit which performs display by a plurality of dots; a coordinate axis display control unit which displays a plurality of coordinate axes (x, y) on the display unit and displays scales at a predetermined scale interval on a predetermined coordinate axis (x) of the coordinate axes (x, y), wherein the plurality of coordinate axes (x, y) include a vertical axis (y) and a horizontal axis (x) which serves as the predetermined coordinate axis; a graph display control unit which displays a graph in a coordinate system determined by the coordinate axes (x, y); and a trace control unit which moves a trace pointer on the graph for a predetermined number of dots at a time in the axis direction of the predetermined coordinate axis (x) according to a user operation and displays a coordinate value of the trace pointer on the display unit, while displaying the trace pointer on the graph; characterized by an image data storing unit (12, 13) which stores at least one image data about an image, wherein a horizontal reference line is defined in the image; an image data designating unit (2, 30) which designates image data of the at least one image data in the image data storing unit (12, 13) based on a user operation; and an image data display control unit which displays the image of the image data designated by the image data designating unit (2, 30) to be superposed on the coordinate system, and in that the graph display apparatus is arranged such that additional data is added to each of the image data, the additional data representing a display range, the display range being indicated by minimum and maximum values of the horizontal and vertical coordinates, set so as to correspond to a width and a height of an image of the image data, the additional data is set in such a way that the reference line of the image is matched with the horizontal axis (x) when the image of the image data is superposed on the coordinate system, the image data display control unit matches the reference line with the horizontal axis (x) based on the additional data and displays the image of the image data designated by the image data designating unit (2, 30) to be superposed on the coordinate system, and a value obtained by subtracting said minimum value from said maximum value of the display range of each of the coordinate axes (x, y) is defined as a numerical width of each of the coordinate axes (x, y), and the coordinate axis display control unit sets the numerical width of the predetermined coordinate axis (x) in such a way that a value obtained by dividing the numerical width of the predetermined coordinate axis (x) by the scale interval is one N-th of a number of dots in an axis direction of the predetermined coordinate axis (x), wherein N is an integer, and displays the predetermined coordinate axis (x). a display unit which performs display by a plurality of dots; a coordinate axis display control unit which displays a plurality of coordinate axes (x, y) on the display unit and displays scales at a predetermined scale interval on a predetermined coordinate axis (x) of the coordinate axes (x, y), wherein the plurality of coordinate axes (x, y) include a vertical axis (y) and a horizontal axis (x) which serves as the predetermined coordinate axis; a graph display control unit which displays a graph in a coordinate system determined by the coordinate axes (x, y); and a trace control unit which moves a trace pointer on the graph for a predetermined number of dots at a time in the axis direction of the predetermined coordinate axis (x) according to a user operation and displays a coordinate value of the trace pointer on the display unit, while displaying the trace pointer on the graph;