Abstract: A device for detecting the inclination of a screen includes a single image sensor detecting voltages in proportion to the brightness of light beams, the light beams being reflected from two positions horizontally or vertically remote from each other on the screen and being incident on the image sensor; a distance measuring section for determining the distances between the image sensor and the two respective positions on the screen from the respective voltages detected by the image sensor; and an inclination angle measuring section for determining the inclination angle of the screen from the distances determined in the distance measuring section. The inclination of the screen can be easily and correctly adjusted through the use of the device.