A device including: a main folding mechanism for folding a diaper body in two at the crotch portion by rotating first and second main pads having first and second holding surfaces, respectively and a sub-folding mechanism for folding the flap by rotating a side pad having a sub-holding surface for holding the flap with respect to the first main pad, wherein a cut-out is formed at a position corresponding to the attachment portion of the second main pad, wherein the cut-out does not allow the attachment portion to be held by the second main pad but instead expose the attachment portion with the first and second holding surfaces being closed while opposing each other and with the main body folded in two, the cut-out allows the flap to be attached to the attachment portion and the side pad rotates from a position where it is open while lying next to the first main pad in the girth direction to a position where the sub-holding surface is closed while opposing the first holding surface, fitting into the cut-out.
