A sheet-supplying device, including: a sheet stacking plate on which plural sheets are stacked; an air-suction sheet conveying mechanism which draws up a sheet and conveys the sheet; an air-suction detecting sensor which detects that the air-suction sheet conveying mechanism has drawn up the sheet; a floating-air blowing section which blows air against side edges of the sheets stacked on the sheet stacking pate to float the sheet; and a control section which controls the floating-air blowing section to conduct a sheet supplying operation, wherein the control section selects a first sheet supplying mode or a second sheet supplying mode, based on at least one of: information of a size of the sheets; information of a thickness of the sheets, and information of a type of the sheets.