Abstract: When conveying an envelope, a posture of the envelope is corrected by hitting a closed portion of the envelope, which is opposite side of an opened portion of the envelope, against a nip portion between upper and lower rollers of the pre-registration rollers and the envelope is then conveyed with the envelope being nipped by the upper and lower rollers of the pre-registration rollers. The upper and lower rollers of the pre-registration rollers nip the envelope to remove air from the envelope. When setting an envelope mode to control a conveying speed of the envelope based on a coverage rate of an image to be formed on the envelope, the conveying speed of the envelope is controlled by adjusting a rotation speed of the registration rollers based on the coverage rate of the set envelope mode.

Abstract: The invention is to provide a sheet accumulation apparatus enabling to uniformly load tabbed sheets into a train of sheets for load and store the sheets on a tray. The sheet accumulation apparatus has a sheet outlet for successively discharging the sheets, a tray means for loading to hold the sheets thereon, a sheet carrier means for discharging the sheets from the sheet outlet to the side of a downstream, a sheet front end regulating means for colliding the sheets sent by the sheet carrier means against the regulating means at the sheet front ends and regulating them, and a sheet rear regulating means disposed to the tray means for regulating the positions of the sheets from the sheet outlet at the sheet rear ends.