A stretchable/contractible sheet having an up-down direction and a left-right direction intersecting each other is provided. The stretchable and contractible sheet includes: a first welded-portion row including a plurality of welded portions arranged side-by-side in the up-down direction； and a second welded-portion row including the plurality of welded portions located adjacent to the first welded-portion row on a one side in the left-right direction. The first welded-portion row includes: a first convex portion protruding toward the one side； and a second convex portion. The second welded-portion row includes a third convex portion protruding toward another side opposite to the one side in the left-right direction.
