A sheet conveying device includes a controller having a processing unit to cause a first detector to detect an uppermost sheet, an elevator to lift and stop a sheet stack at a reference position, and a second detector to detect and store the position. In a primary operation of the controller, the uppermost sheet is attracted and conveyed for a given number of times while the second detector contacting it, a variation amount of angle is calculated and converted to a thickness of M sheets. With a driven contact roller retracted in a secondary operation, the sheet stack is lifted each time the uppermost sheets by a thickness of N sheets are attracted and conveyed based on the stored thickness of M sheets under N=XM (“M” represents a positive number, “N” represents a positive integer, and “X” represents a positive number of 1 or greater).