A disposable diaper includes a semi-rigid absorbent body and high flexible side flaps disposed on laterally opposite side thereof. Each of said side flaps includes a first flap disposed outside said absorbent body and a second flap diverged from said first side flap. Each of said second flaps has the associated one of an elastic band incorporated therein and turned up under an elastic effect of said associated elastic band at least along a line of the divergence.