A sheet processing apparatus, comprising: a processing tray on which sheets transported in a predetermined delivery direction (d) are accumulated; a binding device configured to bind one side on an upstream side in the delivery direction (d) of the sheets accumulated on the processing tray; a gripping device configured to grip the one side of the sheets bound by the binding device; a first moving mechanism (SM, SB1, SB2, 120, SG1, SG2, SP1-SP4) configured to move the binding device in a direction (a, b) intersecting the delivery direction (d) along the one side of the sheets accumulated on the processing tray; and a second moving mechanism (GM2, GB, GP1, GP2, GZ11~GZ13) configured to move the sheets in the delivery direction (d) by moving the gripping device in the delivery direction (d) at a time of delivering the sheets, and a control unit configured to control the binding device by the first moving mechanism (SM, SB1, SB2, 120, SG1, SG2, SP1-SP4) and control the gripping device by the second moving mechanism (GM2, GB, GP1, GP2, GZ11~GZ13), characterized in that, in a case that the binding device is moved by the first moving mechanism (SM, SB1, SB2, 120, SG1, SG2, SP1-SP4) to an opposite side of the gripping device in a direction along the one side, the control unit causes the second moving mechanism (GM2, GB, GP1, GP2, GZ11~GZ13) to move the gripping device to a retreat position at which the gripping device is prevented from prohibiting movement of the binding device, before a first sheet of a sheet bundle to be stacked is transported to the processing tray, and the control unit causes the second moving mechanism (GM2, GB, GP1, GP2, GZ11~GZ13) to move the gripping device to a region at which the binding device moves, after the binding device is moved to the opposite side of the gripping device. a processing tray on which sheets transported in a predetermined delivery direction (d) are accumulated; a binding device configured to bind one side on an upstream side in the delivery direction (d) of the sheets accumulated on the processing tray; a gripping device configured to grip the one side of the sheets bound by the binding device; a first moving mechanism (SM, SB1, SB2, 120, SG1, SG2, SP1-SP4) configured to move the binding device in a direction (a, b) intersecting the delivery direction (d) along the one side of the sheets accumulated on the processing tray; and a second moving mechanism (GM2, GB, GP1, GP2, GZ11~GZ13) configured to move the sheets in the delivery direction (d) by moving the gripping device in the delivery direction (d) at a time of delivering the sheets, and a control unit configured to control the binding device by the first moving mechanism (SM, SB1, SB2, 120, SG1, SG2, SP1-SP4) and control the gripping device by the second moving mechanism (GM2, GB, GP1, GP2, GZ11~GZ13), characterized in that, in a case that the binding device is moved by the first moving mechanism (SM, SB1, SB2, 120, SG1, SG2, SP1-SP4) to an opposite side of the gripping device in a direction along the one side, the control unit causes the second moving mechanism (GM2, GB, GP1, GP2, GZ11~GZ13) to move the gripping device to a retreat position at which the gripping device is prevented from prohibiting movement of the binding device, before a first sheet of a sheet bundle to be stacked is transported to the processing tray, and the control unit causes the second moving mechanism (GM2, GB, GP1, GP2, GZ11~GZ13) to move the gripping device to a region at which the binding device moves, after the binding device is moved to the opposite side of the gripping device.