Patent ID: 7905473

Claim:
A sheet creaser comprising: a pressing unit that presses a folded side of a stack of sheets folded by a folding unit, thereby making a strong crease on the stack of sheets, the pressing unit including a pressure roller that slides on the folded side while rotating, an elastic biasing unit that presses the pressure roller in a thickness direction of the stack of sheets, and a driving unit that slides the pressure roller in a direction substantially perpendicular to a conveying direction of the stack of sheets; and a lifting unit that, when the pressure roller slides to a first position, temporarily lifts up the pressure roller, and when lifted-up pressure roller slides to a second position, lifts the lifted-up pressure roller down onto the folded side, wherein the first position and the second position are located before a corner of the folded side, whereby the pressure roller cannot slide up on the folded side, wherein the lifting unit is a cam mechanism, and when the pressure roller is sliding from a home position toward the folded side, a part of the pressure roller slides on the lifting unit before the corner of the folded side so that the lifting unit lifts up the pressure roller above the stack of sheets, wherein the cam mechanism includes a first guiding member that is attached to the pressure roller as a projection, a second guiding member on which a lower surface of the first guiding member slides so that the pressure roller is lifted up and down, and a position adjusting unit that adjusts the first position and the second position by moving the second guiding member in a sliding direction of the first guiding member to a stand-by position.