Abstract: A three-dimensional graphic displaying system and its method allow a viewpoint to a displayed graphic to change when the displayed graphic is rotated or moved. By including a data generating unit for generating scale mark data for respective variable values corresponding to each coordinate axis, as a combination of two or more lines which exist on a plane perpendicular to a coordinate axis, and are not located on an identical straight line; a viewpoint converting unit for converting the generated data into data of a coordinate system which varies depending on a position of a user viewpoint; and a displaying unit for two-dimensionalizing the converted data, and displaying the two-dimensionalized data on a display unit in correspondence with the position of the user viewpoint, the positions of the scale marks can be identified even if the viewpoint exists in an extended portion of the scale marks on the coordinate axis.