Post processing device, recording system, and method for controlling post processing device

A post processing device that performs post processing on a medium recorded on by a recording device, the post processing device comprising:

• a processing tray configured to support a medium on which post processing is to be performed;
• a post processing section configured to perform post processing on the medium supported by the processing tray;
• and
• a blowing section configured to blow air at the medium supported by the processing tray, wherein:
• the medium supported by the processing tray has a first region supported by the processing tray and a second region not supported by the processing tray and
• the blowing section blows air toward the second region of the medium on which the post processing has not been executed by the post processing section;
• and
• a control section for controlling the blowing section
• sets a blowing amount by the blowing section to a first blowing amount when a number of sheets of medium supported by the processing tray is less than a predetermined set number of sheets and
• sets a blowing amount by the blowing section to a second blowing amount, which is larger than the first blowing amount, when the number of sheets of medium supported by the processing tray is equal to or greater than the set number of sheets.