A sheet-material supply device comprising: a lift to elevate sheet materials in a stacked state; a sheet-material detector to detect that an uppermost sheet material of the sheet materials in the stacked state has reached a predetermined height; and a sheet-material retaining conveyor to retain and convey the uppermost sheet material that has reached the predetermined height, wherein the sheet-material supply device stops elevation of the sheet materials in the stacked state when the sheet-material detector detects that the uppermost sheet material has reached the predetermined height, and wherein the sheet-material retaining conveyor is disposed to be movable in a direction in which the sheet materials in the stacked state elevate, an elevation detector to detect elevation of the sheet-material retaining conveyor from a retaining position at which the sheet-material retaining conveyor retains the uppermost sheet material that has reached the predetermined height; and a controller to control elevation of the sheet materials in the stacked state to stop when the elevation detector detects elevation of the sheet-material retaining conveyor; characterized in that the sheet-material supply device includes a plurality of sheet-material retaining conveyors, including the sheet-material retaining conveyor, to retain a plurality of portions of the uppermost sheet material different from each other in a plane direction of the uppermost sheet material, wherein the sheet-material supply device includes a plurality of elevation detectors, including the elevation detector, to detect elevation of the plurality of sheet-material retaining conveyors, and wherein the controller controls elevation of the sheet materials in the stacked state to stop when at least one of the plurality of elevation detectors detects elevation of at least one of the plurality of sheet-material retaining conveyors. a lift to elevate sheet materials in a stacked state; a sheet-material detector to detect that an uppermost sheet material of the sheet materials in the stacked state has reached a predetermined height; and a sheet-material retaining conveyor to retain and convey the uppermost sheet material that has reached the predetermined height, wherein the sheet-material supply device stops elevation of the sheet materials in the stacked state when the sheet-material detector detects that the uppermost sheet material has reached the predetermined height, and wherein the sheet-material retaining conveyor is disposed to be movable in a direction in which the sheet materials in the stacked state elevate, an elevation detector to detect elevation of the sheet-material retaining conveyor from a retaining position at which the sheet-material retaining conveyor retains the uppermost sheet material that has reached the predetermined height; and a controller to control elevation of the sheet materials in the stacked state to stop when the elevation detector detects elevation of the sheet-material retaining conveyor; characterized in that the sheet-material supply device includes a plurality of sheet-material retaining conveyors, including the sheet-material retaining conveyor, to retain a plurality of portions of the uppermost sheet material different from each other in a plane direction of the uppermost sheet material, wherein the sheet-material supply device includes a plurality of elevation detectors, including the elevation detector, to detect elevation of the plurality of sheet-material retaining conveyors, and wherein the controller controls elevation of the sheet materials in the stacked state to stop when at least one of the plurality of elevation detectors detects elevation of at least one of the plurality of sheet-material retaining conveyors.