Patent ID: 8333371

Claim:
A creasing device for making a crease on one sheet each, the creasing device comprising: a first member on which a linear convex-edged blade is formed in a direction perpendicular to a sheet conveying direction; a second member on which a concave-edged blade pairing with the convex-edged blade is formed; and a drive unit that drives the first and second members to relatively come close to and away from each other, thereby causing the first member and second member to hold the sheet that is stopped at a set position therebetween and make a crease on the sheet, wherein when in a standby state, the drive unit keeps the first member and second member in a state where a face of the convex-edged blade to have contact with the sheet is tilted so that a back side of the convex-edge blade is closer to the second member than a front side of the convex-edge blade; and at the time of making a crease on the sheet, the drive unit causes the first member and second member to be in a state where the convex-edged blade and the concave-edged blade have point contact with each other via the sheet held therebetween so as to initiate a creasing movement by a rotation movement thereof.