Sheet processing apparatus and image forming system having plural roller pairs

A sheet processing apparatus, comprising:

• a conveyance roller pair that rotates in a certain direction to convey a sheet;
• a first normal-reverse rotation roller pair that is capable of rotating in a normal direction and a reverse direction and rotates to convey the sheet;
• a first driver that drives the first normal-reverse rotation roller pair to rotate;
• a first driving force transmitter that transmits a driving force of the first driver for rotating the first normal-reverse rotation roller pair in a first specific direction to the conveyance roller pair so as to rotate the conveyance roller pair in the certain direction, and blocks a driving force of the first driver for rotating the first normal-reverse rotation roller pair in the direction opposite to the first specific direction from being transmitted to the conveyance roller pair;
• a second normal-reverse rotation roller pair that is capable of rotating in a normal direction and a reverse direction and rotates to convey the sheet;
• a second driver that drives the second normal-reverse rotation roller pair to rotate;
• and
• a second driving force transmitter that transmits a driving force of the second driver for rotating the second normal-reverse rotation roller pair in a second specific direction to the conveyance roller pair so as to rotate the conveyance roller pair in the certain direction, and blocks a driving force of the second driver for rotating the second normal-reverse rotation roller pair in the direction opposite to the second specific direction from being transmitted to the conveyance roller pair.