In order to accurately maintain an interval between a preceding sheet and a subsequent sheet, a sheet conveying device effects control such that, under the condition that a trailing end sensor disposed on a conveying path for supply has detected a trailing end of the preceding sheet, the subsequent sheet is conveyed at a high-speed conveying speed at a fixed time, and such that, under the condition that a leading end sensor has detected a leading end of a sheet, switches a detected sheet from the high-speed to a low-speed conveying speed at a fixed time and conveys the detected sheet.