To perform an optimal file folding according to user's request.

A folding device includes a first step (S501-S503) of receiving an input of the size of a recording medium when performing multiple folding by a computer; a second step (S511, S512) of receiving a setting of the size of a final surface of the folded recording medium; a third step (S521, S522) of receiving an input of presence of punch drilling to the recording medium; and a fourth step of performing the folding by changing the folding position of the multiple folding to the recording medium, based on the size of the recording medium, the size of the final surface, and the presence of the punch drilling. The device also determines a folding position by the steps to a conveyed sheet, performs the folding, and enables the file folding.