Method for manufacturing shopping bags from sealable plastic material with two handles, in particular bags provided with side bellows, which comprises spreading apart the walls of the bag, introducing inside the bag the handle portions to be welded onto the said walls along a direction opposite to the bag movement direction, bring the walls of the bag into contacting relationship with the handles, simultaneously welding the handles and releasing the bag provided with its handles in the bag movement direction, the device for working such method which comprises feeding means for the bags with a stepwise movement so as to bring one by one the bag opening directed along the feeding direction, under sealing jaws for on the one hand, spreading the bag walls from one another adjacent the opening thereof and on the other hand, releasing said walls, and means for simultaneously introducing inside the bag, those parts of both handles which are to be joined to the inner sides of the bag walls.