Abstract: To correct the size of an image projected on a screen surface that is at an oblique angle to a line of projection of a projector, the image is corrected by manual or automatic angular position adjustment of a LCD panel or a mirror. A device for adjusting the image size includes a detector for projecting infrared rays into the screen over a range of projection angles and sensing the amount of infrared rays reflected by the screen. A controller determines a correction angle that is equal to the oblique angle between the screen and the line of projection by observing when the sensed reflected infrared rays reach a maximum amount. A driver, responsive to the controller, then adjusts the angular position of the LCD panel or the mirror by the magnitude of the correction angle, such as to adjust the line of projection into orthogonal relation with the screen.