Sheet processing apparatus and image forming apparatus for stably aligning sheets having a long length

An image forming apparatus, comprising:

• an image forming portion configured to form an image on a sheet;
• a conveyance portion configured to convey a sheet on which an image is formed by the image forming portion, in a sheet conveyance direction;
• a sheet stacking portion configured to stack a sheet conveyed by the conveyance portion;
• a sheet supporting portion arranged downstream of the sheet stacking portion in the sheet conveyance direction and configured to support side edges of the sheet in a width direction perpendicular to the sheet conveyance direction;
• and
• an alignment unit arranged on one side of the sheet supporting portion in the width direction and configured to align the position of the sheet supported by the sheet supporting portion in the width direction by moving toward a center side in the width direction,
• wherein the alignment unit comprises:
• an upstream-side pressing portion configured to press a side edge of the sheet supported by the sheet supporting portion in the width direction;
• and
• a downstream-side pressing portion arranged downstream of the upstream-side pressing portion in the sheet conveyance direction and configured to press the side edge of the sheet supported by the sheet supporting portion, and
• wherein the downstream-side pressing portion comprises:
• a first pressing portion arranged downstream of the center of gravity of a predetermined-size sheet supported by the sheet supporting portion in the sheet conveyance direction and upstream of a downstream edge of the predetermined-size sheet in the sheet conveyance direction and configured to press the predetermined-size sheet;
• and
• a second pressing portion arranged downstream of the downstream edge of the predetermined-size sheet supported by the sheet supporting portion in the sheet conveyance direction and downstream of the center of gravity of a large-size sheet having twice or more than twice the length of the predetermined-size sheet and configured to press the large-size sheet, the second pressing portion being formed to protrude further toward the center side in the width direction than the first pressing portion.