PROBLEM TO BE SOLVED: To provide a disposable diaper production method facilitating cause investigation of incidence of defects.SOLUTION: The production method is disclosed for producing a disposable diaper 100 in which both width-directional left/right sides of a front piece and a back piece are mutually joined by side seal parts 4. A step of forming the side seal parts 4 includes sequentially pressing and fusing a plurality of blocks 51 provided in a seal device 50 onto both width-directional left/right sides of the front piece and the back piece so as to form the side seal parts 4. The plurality of blocks 51 include different joining patterns respectively for joining the front piece and the back piece.
