A sheet post-processing apparatus, comprising: a transport roller configured to transport sheets; a processing tray configured to hold the sheets transported by the transport roller; a stopper that is disposed on an upstream side of the processing tray in a sheet transport direction; a paddle member configured to rotate around a rotating shaft, the rotating shaft being disposed in a sheet width direction of the sheets held on the processing tray, the sheet width direction being orthogonal to the sheet transport direction, the rotating paddle member pressing the sheets held on the processing tray against the stopper and aligning ends of the sheets misaligned in the sheet transport direction; and a controller configured to: stop rotation of the paddle member in a state that the paddle member comes in contact with the sheets held on the processing tray, drive the transport roller to transport subsequent sheets to the processing tray, rotate the paddle member from a standby position where transport of the sheets is not hindered when the sheets are transported to the processing tray, control the paddle member to come in contact with the sheets, control the paddle member to apply a force on the sheets to move toward the processing tray, further rotate the paddle member; control the paddle member to press the sheets against the stopper, control the paddle member to align the ends of the sheets misaligned in the sheet transport direction, and after the ends of the sheets misaligned in the sheet transport direction are aligned, stop the rotation of the paddle member at a first stop position where the paddle member does not come in contact with the sheets held on the processing tray, characterized in that the controller is further configured to: after the controller stops the rotation of the paddle member at the first stop position and a predetermined time elapses, rotate again the paddle member, control the paddle member to press the sheets against the stopper, and control the paddle member to align again the ends of the sheets misaligned in the sheet transport direction. a transport roller configured to transport sheets; a processing tray configured to hold the sheets transported by the transport roller; a stopper that is disposed on an upstream side of the processing tray in a sheet transport direction; a paddle member configured to rotate around a rotating shaft, the rotating shaft being disposed in a sheet width direction of the sheets held on the processing tray, the sheet width direction being orthogonal to the sheet transport direction, the rotating paddle member pressing the sheets held on the processing tray against the stopper and aligning ends of the sheets misaligned in the sheet transport direction; and a controller configured to: stop rotation of the paddle member in a state that the paddle member comes in contact with the sheets held on the processing tray, drive the transport roller to transport subsequent sheets to the processing tray, rotate the paddle member from a standby position where transport of the sheets is not hindered when the sheets are transported to the processing tray, control the paddle member to come in contact with the sheets, control the paddle member to apply a force on the sheets to move toward the processing tray, further rotate the paddle member; control the paddle member to press the sheets against the stopper, control the paddle member to align the ends of the sheets misaligned in the sheet transport direction, and after the ends of the sheets misaligned in the sheet transport direction are aligned, stop the rotation of the paddle member at a first stop position where the paddle member does not come in contact with the sheets held on the processing tray, stop rotation of the paddle member in a state that the paddle member comes in contact with the sheets held on the processing tray, drive the transport roller to transport subsequent sheets to the processing tray, rotate the paddle member from a standby position where transport of the sheets is not hindered when the sheets are transported to the processing tray, control the paddle member to come in contact with the sheets, control the paddle member to apply a force on the sheets to move toward the processing tray, further rotate the paddle member; control the paddle member to press the sheets against the stopper, control the paddle member to align the ends of the sheets misaligned in the sheet transport direction, and after the ends of the sheets misaligned in the sheet transport direction are aligned, stop the rotation of the paddle member at a first stop position where the paddle member does not come in contact with the sheets held on the processing tray, characterized in that the controller is further configured to: after the controller stops the rotation of the paddle member at the first stop position and a predetermined time elapses, rotate again the paddle member, control the paddle member to press the sheets against the stopper, and control the paddle member to align again the ends of the sheets misaligned in the sheet transport direction. after the controller stops the rotation of the paddle member at the first stop position and a predetermined time elapses, rotate again the paddle member, control the paddle member to press the sheets against the stopper, and control the paddle member to align again the ends of the sheets misaligned in the sheet transport direction.