An apparatus includes a first rotary disc, a plurality of folding plates arranged at regular intervals along a peripheral zone of the first rotary disc, a plurality of positive motion cams arranged at regular intervals along the peripheral zone of the first rotary disc so as to be interposed between the first rotary disc and the folding plates, a second rotary disc located on the opposite side of the first rotary disc and a plurality of auxiliary plates arranged at regular intervals along a peripheral zone of the second rotary disc. One of the folding plates and one of the auxiliary plates synchronously move into the inside of a contiguous diaper structure and simultaneously the guide arms move into a clearance between the guide blades so that the opposite side edge zones of the crotch region may be held between the guide arms and the guide blades and thereby the crotch region may be tucked into the contiguous diaper structure.