Patent ID: 7650823

Claim:
A punch unit comprising: a punching section configured to punch a sheet transported; a detecting unit which detects the position of a lateral edge of the sheet; correction-amount calculating means for performing addition or subtraction on data detected by the detecting unit, in order to eliminate the displacement of the center of the punching section, which occurs in a direction at right angles to the sheet-transporting direction when the punching section is inclined; and a punching-section rotating mechanism which has a rotation center existing outside the maximum width of the sheet and which rotates the punching section back and forth in the direction in which the sheet is transported, and a lever shaft that rotates a tongue strip in accordance with the rotation of a longitudinal-registering motor, wherein the tongue strip of the punching-section rotating mechanism intersects at a right angle with the direction in which the sheet is transported and rotates in a longitudinal direction, wherein the punching-section rotating mechanism has an adjusting motor for adjusting rotation to rotate the punching-section in the direction which the sheet is transported when controlled by a control unit, an idler gear for transmitting the rotation of the motor, and a gear set in mesh with the idler gear and having a lever shaft which stands to engage an elongated hole which is provided in with the punching section in which the lever shaft is at one end of the idler gear and rotates a tongue strip to enable the punching-section rotating mechanism to move in the longitudinal direction.