A bag includes: a film defining a containable space and a first area and a second area both facing the containable space; an elongated tearing guide piece directly or indirectly bonded to the first area; an elongated belt-shaped base disposed between the tearing guide piece and the second area and along the tearing guide piece; a tab defined by a cut portion penetrating through the first area of the film, the tearing guide piece and the belt-shaped base; and a surrounding seal area intersecting the tearing guide piece in a width direction, the surrounding seal area bonding the first area and the second area to define an area surrounding the tab.