A sheet supplying device has a sheet delivering roller for delivering sheets one by one; a feeding roller for feeding the sheet delivered by the sheet delivering roller; a pinch roller urged by the feeding roller to be rotated by the feeding roller; a detecting lever swingable by being contacted by a leading of the sheet delivered by the sheet delivering roller; and a sensor for detecting the swing motion of the detecting lever. An area of said detecting lever to which the leading end of the sheet is contactable is such a curved surface that a distance from a nip between the feeding roller and the pinch roller is substantially constant.