An image-forming apparatus contains an image-forming portion, a first conveying portion that is arranged at an upstream side of the image-forming portion along a sheet conveying direction, a second conveying portion that is arranged at an upstream side of the first conveying portion along the sheet conveying direction and a control portion. The control portion controls the first conveying portion to move a pair of registration rollers along a direction that is orthogonal to the sheet conveying direction while the pair of registration rollers nips the sheet when conveying the sheet to the image-forming portion. The control portion controls the second conveying portion to move one of the pair of conveying rollers along the direction that is orthogonal to the sheet conveying direction while the pair of conveying rollers does not nip the sheet.

An image forming device comprising: a feeder that feeds a sheet; a resisting unit that corrects skew of the sheet fed by the feeder and carries the sheet toward downstream side; a detector that detects the sheet carried toward downstream side by the resisting unit after the skew of the sheet is corrected; and a hardware processor that drives the feeder and the resisting unit, respectively. The hardware processor starts driving the resisting unit before the sheet fed by the feeder reaches the resisting unit.

The sheet stacker includes a sheet conveyor arrangement, configured for feeding a plurality of sheets and having a sheet discharge end, and a stacking bay. In the stacking bay sheets delivered by the sheet conveyor arrangement are formed into stacks. A stack conveyor is provided in the stacking bay and is movable in a conveyor direction parallel to a sheet feeding direction, according to which the sheets are fed from the sheet discharge end onto the stack conveyor. The sheet discharge end is configured and controlled such that it is gradually lifted during sheet stacking, in order to accommodate a growing stack of sheets being formed on the stack conveyor. A stop plate is positioned in the stacking bay above the stack conveyor and in front of the sheet discharge end of the sheet conveyor arrangement. The stop plate is configured and controlled to be gradually lifted from the stack conveyor as the sheet stack grows, to be withdrawn upon completion of the stack thus allowing removal of the stack in an evacuation direction substantially parallel to the conveyor direction, and to be lowered towards the stack conveyor again.

The sheet stacker includes a sheet conveyor arrangement, configured for feeding a plurality of sheets and having a sheet discharge end, and a stacking bay. In the stacking bay sheets delivered by the sheet conveyor arrangement are formed into stacks. A stack conveyor is provided in the stacking bay and is movable in a conveyor direction parallel to a sheet feeding direction, according to which the sheets are fed from the sheet discharge end onto the stack conveyor. The sheet discharge end is configured and controlled such that it is gradually lifted during sheet stacking, in order to accommodate a growing stack of sheets being formed on the stack conveyor. A stop plate is positioned in the stacking bay above the stack conveyor and in front of the sheet discharge end of the sheet conveyor arrangement. The stop plate is configured and controlled to be gradually lifted from the stack conveyor as the sheet stack grows, to be withdrawn upon completion of the stack thus allowing removal of the stack in an evacuation direction substantially parallel to the conveyor direction, and to be lowered towards the stack conveyor again.

A sheet post-processing apparatus includes: a sheet stack tray; a rear-end-position regulating member, against which a rear end of the sheet on the tray is butted to align a position of the sheet in a sheet conveying direction to the stack tray, the rear end of the sheet being a rear end in the conveying direction; and a roller member that comes in contact with an upper surface of the sheet conveyed to an upper side of the tray, before the sheet is stacked on a stacking surface on the tray, and conveys the sheet stacked on the stacking surface toward the rear-end-position regulating member, wherein a rotation speed before stacking is set to be smaller than a rotation speed after stacking, and the rotation speed of before stacking is greater than zero.