A sheet processing apparatus includes a main conveyance passage, a first branched conveyance passage in a first direction, a second branched conveyance passages in a second direction, a sheet separation device, and a winder. The sheet separation device conveys a first sheet to the first branched conveyance passage, and a second sheet to the second branched conveyance passage to rotate and wind one of the first sheet and the second sheet. The winder is disposed on at least one of the first or second branched conveyance passage and includes a gripper attached to the winder to grip a leading end, in one of first and second directions, of one of the first and second sheets conveyed to corresponding one of the first and second branched conveyance passages.