In copying apparatus having a magnification ratio varying device, wherein a photosensitive member in motion is exposed to an optical image of an original by slit exposing to form an electrostatic latent image thereon and the original scanning velocity is varied in accordance with the magnification ratio selected, it is necessary to effect registration of the forward end of the image of an original with the leading end of a photosensitive sheet or a transfer-printing sheet. The above-mentioned registration is effected by delivering a copy sheet after lapse of a predetermined period of time following the production of a detection signal by a detector, the above-mentioned predetermined period of time being varied in conformity with the selected one of magnification ratios.