Perforation device, post-processing apparatus, and image forming system

A perforation device, comprising:

• a plurality of punches which punch holes on a sheet by a reciprocation motion;
• a holding member which holds the punches in a line in a width direction of the sheet;
• a plurality of dies being arranged opposing to the plurality of the punches;
• a drive shaft to be rotary driven by a driving device;
• two cranks being arranged with phases of an angle being displaced with each other in a shaft rotating direction of the drive shaft, to rotate together with the drive shaft;
• and
• two connection poles connecting with the two cranks and the holding member,
• wherein the two cranks are rotatable to reciprocate the holding member with phases at ends thereof being displaced in order to carry out a differential perforation of cut-outs with a time difference among perforations by each of the punches;
• wherein the reciprocation of the holding member continues in both directions at least until each of the punches reaches a perforation position where the punches perforate the sheet;
• and
• wherein holding positions of predetermined punches, among the punches held by the holding member, are displaced in a reciprocation direction with respect to the holding member, and wherein a lower most position which each of the punches reaches at differential perforation falls within a predetermined range.