A sheet processing apparatus includes a folding roller pair, a sheet pushing member, a detection unit, and a control unit. The folding roller pair folds a sheet or a sheet bundle by a nip portion and conveys a folded sheet or a folded sheet bundle. The sheet pushing member performs a pushing operation in which a tip of the sheet pushing member pushes the sheet or the sheet bundle into the nip portion of the folding roller pair. The detection unit detects whether the tip of the sheet pushing member reaches a predetermined position in a moving direction of the sheet pushing member. The control unit controls driving of the sheet pushing member according to a result of detection by the detection unit such that the sheet pushing member repeats the pushing operation until the detection unit detects that the tip of the sheet pushing member reaches the predetermined position.