A method of manufacturing a disposable diaper in which the position of an absorption core does not become misaligned from the center of a pair of leg elastic members. The method includes a sheet member manufacturing process (P1), a joining process (P2), and a cutting process (P3). In the sheet member manufacturing process (P1), elastic members are joined, while being stretched, to sheets continuously supplied in the machine direction (MD), and this forms belly side and back side sheet members (20, 30). In the joining process (P2), absorptive panels (4) are joined to the belly side and back side sheet members (20, 30) at constant intervals. Each absorptive panel (4) has a pair of crotch elastic members (42) mounted, while being stretched, on the absorptive panel (4) so as to extend along opposite long sides of a rectangular shape of the absorptive panel (4), and also has the absorption core (5) joined to the absorptive panel (4) so as to be symmetrical about an imaginary center line bisecting the distance between the pair of crotch elastic members. In the cutting process (P3), the belly side and back side sheets (2, 3) to which the absorptive panels are joined are cut.
