PROBLEM TO BE SOLVED: To provide an underpants type disposable diaper which can suppress leakage of excretion and which allows a user to pass his/her legs into the underpants type disposable diaper.SOLUTION: An underpants type disposable diaper (1) comprises an absorbent body (10), a belly side waistline part (3) and a back side waistline part (4). A non-skin side of the absorbent body (10) comprises an exterior body (20), and a leakage prevention wall (50) is provided on each of both sides of the absorbent body (10) in a lateral direction. The leakage prevention wall (50) comprises a junction (61) where one side surfaces in the thickness direction are jointed, and a non-junction (62) where surfaces in the thickness direction are not jointed. When the exterior body (20) and the leakage prevention wall (50) are extended to outside of a lateral direction so that a length in the lateral direction of each of the exterior body (20) and the leakage prevention walls (50) becomes maximum, at a position (P20) where the length in the lateral direction of each of them becomes minimum, a projection amount (W21) of the exterior body (20) from an outermost end (10e) of the absorbent body (10) in the lateral direction is smaller than a projection amount (W50) of the leakage prevention wall (50) from the outermost end (10e).SELECTED DRAWING: Figure 6
