Angle detecting apparatus and projector equipped therewith automatically correcting the Keystone distortion

In an angle detecting apparatus and projector using range finders, range finding calculations are performed in plural directions using line type passive range finders as a range finding portion. Thus, if one range finding result is an abnormal value, the effects are reduced. The structure is miniaturized. ÄMeans for ResolutionÜ A control circuit 5 calculates four horizontal relative inclination angles between a screen 1 and a projector 2 based on results of range finding calculations of a line type passive range finder 3 doing range finding in five directions, finds their average value, calculates four vertical relative inclination angles between the screen 1 and the projector 2 based on the results of range finding of a line type passive range finder 4 doing range finding in five directions, and finds their average value. A display driving portion 7 adjusts a projection optical system 8 including a condensing lens based on the horizontal and vertical inclination angles calculated by the control circuit 5 and on the distance between range finding calculational regions, thus correcting keystone distortion in the projected image.