To obtain an apparatus and a method for producing bags, in each of which a plastic bag can be mass-produced by folding a tubular resin material in two in the direction perpendicular to the center axis of a tube and welding one end of the folded tube.

The long tube, which is unwound from a resin roll obtained by winding the resin-made, thin and flexible tube in a state squashed into a prescribed-width long tube-like shape, is folded successively by first and second folding unit 12, 13 in the direction perpendicular to the conveying direction. The folded long tube is heat-sealed at prescribed intervals by a heat sealing unit 14. The heat-sealed long tube is cut by a cutting unit 15 to obtain the plastic bags.