It is a stretchable/contractible sheet (31) in which a plurality of elastic members (35) are arranged between the first sheet (32) and the second sheet (33) joined by a plurality of welded portions (50). The stretchable/contractible sheet (31) includes: the first welded-portion row (61) having a plurality of welded portions (50) arranged side-by-side in the up-down direction； and a second welded-portion row (62) arranged adjacent to the first welded-portion row (61) on the one side in the left-right direction. The first welded-portion row (61) includes: a first convex portion (61P1) projecting toward the one side； and a second convex portion (61P2). The second welded-portion row (62) includes a third convex portion (62P3) projecting toward the other side in the left-right direction. In the natural state, a other-side end (62P3C) of the third convex portion (62P3) is located on the other side with respect to a straight line connecting a one-side end (61P1A) of the first convex portion (61P1) and a one-side end (61P2B) of the second convex portion (61P2).
