Abstract: Apparatus is disclosed for use with image forming apparatus having a pair of galvanometers one of which, in response to a ramp signal rotates a mirror which scans lines in one direction across the image and the other of which in response to a staircase signal rotates another mirror in a direction perpendicular to the direction of the lines to scan successive ones of the lines. The apparatus includes circuits responsive to the galvanometer drive signal amplitudes for producing a compensating signal which is representative of the angular displacement of the mirrors and thus of the position to which the beam is scanned at any instant. This compensating signal and the signal which drives the galvanometer which scans the beam between successive lines are combined to adjust the angular displacement of the mirror which scans the beam in the direction between the successive lines, thus correcting the geometric distortion of the pin cushion type of the image.