Sheet supply device and image forming system

An image forming system comprising:

• an image forming apparatus configured to form an image on a sheet and provided with an output gear configured to output a driving force to an outside;
• and
• a sheet supply device configured to be attached to and detached from the image forming apparatus, the sheet supply device being configured to receive the driving force from the image forming apparatus to supply a sheet to the image forming apparatus in response to attachment of the sheet supply device to the image forming apparatus, the sheet supply device comprising:
• a main body provided with a sheet supply tray on which a sheet is mountable;
• a sheet supply roller configured to be in contact with a sheet mounted on the sheet supply tray and configured to rotate to supply the sheet toward the image forming apparatus;
• an external output gear;
• a clutch mechanism configured to transmit and interrupt the driving force received from the image forming apparatus to the sheet supply roller and the external output gear;
• a first transmission mechanism configured to transmit the driving force received through the clutch mechanism to the sheet supply roller;
• and
• a second transmission mechanism configured to transmit the driving force received through the clutch mechanism to the external output gear, the external output gear being configured to output the driving force received from the second transmission mechanism to an outside.