An apparatus for successively making plastic bags each of which includes an end surface provided with a protrusion, the protrusion being provided with an inlet port, the apparatus comprising: a panel material feeding device by which first and second webs of panel material (1, 2) are superposed on each other and fed longitudinally thereof; a panel material guide device by which the first and second webs of panel material (1, 2) are guided when being fed so that the first web of panel material is folded along a first folded line at a position adjacent to a side edge of first web of panel material while the second web of panel material is folded along a second folded line at a position adjacent to a corresponding side edge of second web of panel material, a first folded portion being formed in the first web of panel material, a second folded portion being formed in the second web of panel material, the first folded portion being superposed on the second folded portion, there existing a distance between the side edge and the first folded line, which is larger than twice a distance between the corresponding side edge and the second folded line by a predetermined distance after the first and second webs of panel material (1, 2) are folded along the first and second folded lines, the side edge and the corresponding side edge being aligned with each other when the first folded portion is superposed on the second folded portion; a slitting blade by which the first web of panel material is slit along the first folded line when being fed after being folded so that an opening is formed in the first folded portion; a cross seal device by which the first and second webs of panel material (1, 2) are heat sealed with each other widthwise of the first and second webs of panel material (1, 2) whenever the first and second webs of panel material (1, 2) are fed intermittently; and a cutter by which the first and second webs of panel material (1, 2) are cut widthwise of the first and second webs of panel material (1, 2) whenever the first and second webs of panel material (1, 2) are fed intermittently, the end surface being formed by the first folded portion, the protrusion being formed by the predetermined distance, the inlet port being formed by the opening. a panel material feeding device by which first and second webs of panel material (1, 2) are superposed on each other and fed longitudinally thereof; a panel material guide device by which the first and second webs of panel material (1, 2) are guided when being fed so that the first web of panel material is folded along a first folded line at a position adjacent to a side edge of first web of panel material while the second web of panel material is folded along a second folded line at a position adjacent to a corresponding side edge of second web of panel material, a first folded portion being formed in the first web of panel material, a second folded portion being formed in the second web of panel material, the first folded portion being superposed on the second folded portion, there existing a distance between the side edge and the first folded line, which is larger than twice a distance between the corresponding side edge and the second folded line by a predetermined distance after the first and second webs of panel material (1, 2) are folded along the first and second folded lines, the side edge and the corresponding side edge being aligned with each other when the first folded portion is superposed on the second folded portion; a slitting blade by which the first web of panel material is slit along the first folded line when being fed after being folded so that an opening is formed in the first folded portion; a cross seal device by which the first and second webs of panel material (1, 2) are heat sealed with each other widthwise of the first and second webs of panel material (1, 2) whenever the first and second webs of panel material (1, 2) are fed intermittently; and a cutter by which the first and second webs of panel material (1, 2) are cut widthwise of the first and second webs of panel material (1, 2) whenever the first and second webs of panel material (1, 2) are fed intermittently, the end surface being formed by the first folded portion, the protrusion being formed by the predetermined distance, the inlet port being formed by the opening.