An input-output coordinate transforming method for an input-integerated display apparatus of a structure in which an input coordinate designating part is integrally combined with a screen of a display device, wherein coordinates inputted through the input coordinate designating part by an operator are subjected to coordinate transformation before being supplied to the display device so as to make an input point on the input coordinate designating means coincide with an output point on the display screen when observed by the operator. The method comprises steps of displaying sequentially a plurality of predetermined reference coordinates on the display screen and inputting through the input coordinate designating part the coordinates of points thereon designated by the operator which points correspond, respectively, to the reference coordinate points, arithmetically determining constants of predetermined coordinate transformation expressions representing correspondence between the input coordinates and the output coordinates on the basis of the plurality of the reference coordinates and the plurality of the corresponding input coordinates, and transforming the input coordinates supplied by the input coordinate designating part into output coordinates to be supplied to the display device in accordance with the coordinate transformation expressions containing the constants determined.