A sheet separation device separates a non-bonding portion of a two-ply sheet in which two sheets are overlapped and bonded together at one end of the two-ply sheet. The sheet separation device includes a separator that includes a first separator and a second separator. The first separator is inserted into a gap between the two sheets of the two-ply sheet. The second separator is inserted between the two sheets at said another end of the two-ply sheet that is opposite to the one end of the two-ply sheet and moves in a width direction of the two-ply sheet after the first separator is inserted into the gap and relatively moves from the one end to said another end.

A sheet separation device separates a non-bonding portion of a two-ply sheet in which two sheets are overlapped and bonded together at one end of the two-ply sheet. The sheet separation device includes a separator that includes a first separator and a second separator. The first separator is inserted into a gap between the two sheets of the two-ply sheet. The second separator is inserted between the two sheets at said another end of the two-ply sheet that is opposite to the one end of the two-ply sheet and moves in a width direction of the two-ply sheet after the first separator is inserted into the gap and relatively moves from the one end to said another end.

An image forming system includes an image forming apparatus, a sheet processing device, and control circuitry. The image forming apparatus forms an image on a sheet. The sheet processing device performs post-processing on the sheet. The sheet processing device includes a first conveyance path through which the sheet is conveyed and subjected to the post-processing and a second conveyance path through which the sheet is conveyed without the post-processing. In response to an instruction of print jobs including both a print job of one or N copies subjected to the post-processing and a print job not subjected to the post-processing, the circuitry executes the job not subjected to the post-processing during execution of an M-th copy of the job subjected to the post-processing and causes the sheet to be conveyed through the second conveyance path, where N is two or greater and M satisfies 1≤M<N.

A sheet separation device separates a non-bonding portion of a two-ply sheet in which two sheets are overlapped and bonded together at one end of the two-ply sheet. The sheet separation device includes a separator that includes a first separator and a second separator. The first separator is inserted into a gap between the two sheets of the two-ply sheet. The second separator is inserted between the two sheets at said another end of the two-ply sheet that is opposite to the one end of the two-ply sheet and moves in a width direction of the two-ply sheet after the first separator is inserted into the gap and relatively moves from the one end to said another end.