A document feeder constituting an image forming apparatus includes a paper feeder to supply a document to a document transport path, a first transporter to transport the document toward image reading positions, and a second transporter to transport the document toward the document discharging tray while supplying the document to the image reading positions. Furthermore, the document feeder includes a motor provided on the first frame, a first driver provided on the first frame and to transmit driving force generated by the motor to the paper feeder and the first transporter, a second driver provided on the second frame and to transmit the driving force generated by the motor to the second transporter, and a second driver to transmit the driving force generated by the motor to the second transporter, and a relay transmission member to transmit the driving force generated by the motor to the second driver.

A sheet feed device includes: a tray provided in a device body in a manner capable of being pulled out and having a loading part that is moved up and down; an extension part attached to the device body to support a portion of a sheet to be fed through the tray; a lifting mechanism that has a lifting/lowering part for moving the loading part up and down and a driving part for lifting and holding the loading part via the lifting/lowering part; and a disconnecting part that disconnects the lifting/lowering part and the driving part when an uncoupling operation is accepted in a state in which the tray is accommodated in the device body.

A conveyance rotating body is rotatably supported by a support member. A second rotational axis at a rotation center of a driven transmission member is disposed at a position different from a position of a first rotational axis. When a feeding unit is attached to a sheet feeding apparatus, a drive transmission member and the driven transmission member engage with each other. When a driving force is transmitted from the drive transmission member to the driven transmission member, the feeding unit receives a force in an attachment direction of the feeding unit and is positioned with respect to the sheet feeding apparatus.

A sheet feed device includes: a tray provided in a device body in a manner capable of being pulled out and having a loading part that is moved up and down; an extension part attached to the device body to support a portion of a sheet to be fed through the tray; a lifting mechanism that has a lifting/lowering part for moving the loading part up and down and a driving part for lifting and holding the loading part via the lifting/lowering part; and a disconnecting part that disconnects the lifting/lowering part and the driving part when an uncoupling operation is accepted in a state in which the tray is accommodated in the device body.

A printing apparatus includes a printing cylinder (14) that can hold sheets (4) and transfer them one by one continuously, first to fourth inkjet heads (41-44), and a feeder unit (2). The printing apparatus includes a speed reducer (72) that switches the speed of the feeder unit (2) between single-sided printing and double-sided printing. In single-sided printing, the feeder unit (2) is driven at a first supply speed at which the sheets (4) are supplied to the printing cylinder (14) one by one continuously, and the printing cylinder (14) is driven at a transfer speed at which the sheets (4) supplied from the feeder unit (2) one by one continuously are transferred. In double-sided printing, the printing cylinder (14) is driven at the transfer speed, and the feeder unit (2) is driven at a second supply speed that is the first supply speed. The printing apparatus that operates stably in both single-sided printing and double-sided printing can be provided.

A printing apparatus includes a printing cylinder (14) that can hold sheets (4) and transfer them one by one continuously, first to fourth inkjet heads (41-44), and a feeder unit (2). The printing apparatus includes a speed reducer (72) that switches the speed of the feeder unit (2) between single-sided printing and double-sided printing. In single-sided printing, the feeder unit (2) is driven at a first supply speed at which the sheets (4) are supplied to the printing cylinder (14) one by one continuously, and the printing cylinder (14) is driven at a transfer speed at which the sheets (4) supplied from the feeder unit (2) one by one continuously are transferred. In double-sided printing, the printing cylinder (14) is driven at the transfer speed, and the feeder unit (2) is driven at a second supply speed that is the first supply speed. The printing apparatus that operates stably in both single-sided printing and double-sided printing can be provided.

An image reading device includes a first roller that is rotatably supported by a frame, a second roller that is supported by the frame in a rotatable and translatable manner and that presses a medium against the first roller, a joint unit that transmits rotation from a drive shaft to the second roller, a drive unit that rotates both the first roller and the drive shaft, and a read unit configured to read an image on a conveyed medium that is conveyed by the rotation of the both of the first roller and the second roller.

An image reading device includes a first roller that is rotatably supported by a frame, a second roller that is supported by the frame in a rotatable and translatable manner and that presses a medium against the first roller, a joint unit that transmits rotation from a drive shaft to the second roller, a drive unit that rotates both the first roller and the drive shaft, and a read unit configured to read an image on a conveyed medium that is conveyed by the rotation of the both of the first roller and the second roller.

A sheet supplier includes: a tray having a support surface; a roller that supplies a sheet supported on the support surface; an arm pivotable about a pivot shaft, extending in a supply direction and toward the support surface, and supports the roller at its pivotal distal end portion; a motor; and a driving-force transmitting mechanism supported by the arm and configured to transmit a driving force supplied from the motor, to the roller. The driving-force transmitting mechanism includes: a rotating member supported by the pivot shaft and configured to be rotated by the driving force supplied from the motor; and a speed changer configured to determine a rotational speed of the roller to a speed different from a rotational speed of the rotating member.

A transmission device includes a driving motor, a separation roller module, a correction roller module, a discharging roller module, a first clutch, a second clutch, a third clutch and a plurality of sensors which are mounted to an automatic sheet feeder. The first clutch is disposed between the driving motor and the separation roller module. The second clutch is disposed between the driving motor and the correction roller module. The third clutch is disposed between the driving motor and the discharging roller module. The plurality of the sensors sense signal variations at the time of a leading end or a tail end of each of the documents passing through the plurality of the sensors, and the plurality of the sensors transmit the signal variations to the first clutch, the second clutch and the third clutch.