an error display device is a device for displaying a translation error and an attitude error associated with a rectilinear motion of a machine element , and includes a reference - motion - trajectory display unit that displays a design motion trajectory , and an error magnification / display unit that magnifies the translation error and the attitude error and displays the magnified errors , wherein the error magnification / display unit calculates a translation error vector including a magnified translation error obtained by multiplying the translation error by a predetermined magnification factor , draws a translation error trajectory including the design motion trajectory and the translation error vector added thereto , calculates an attitude error matrix including a magnified attitude error obtained by multiplying the attitude error by a predetermined magnification factor , and draws a predetermined shape with coordinates transformed using the attitude error matrix and the translation error vector .