An apparatus for successively making plastic bags each of which includes front, back, one end and other end surfaces, the apparatus comprising: a panel material feed device configured to superpose a web of a first panel material on a web of a second panel material and then feed the webs of the first and second panel materials (1, 2) longitudinally thereof; the apparatus being characterized by a first slit device configured to slit a plastic film along a longitudinal slit line so as to divide the plastic film into the web of the first panel material and a wide web of a bottom gusset material before the webs of first and second panel materials (1, 2) are superposed on each other, the webs of the first and second panel materials (1, 2) being superposed on each other and fed longitudinally after divided; a bottom gusset material feed device configured to feed the wide web of the bottom gusset material longitudinally after divided; a second slit device configured to further slit the wide web of the bottom gusset material so as to divide the wide web of the bottom gusset material into three webs of the bottom gusset material (3, 4); and a bottom gusset material guide device configured to guide and supply the three webs of the bottom gusset material (3, 4) to the web of the first or second panel material (1, 2), the bottom gusset material guide device being disposed a downstream side of the second slit device; wherein the three webs of the bottom gusset material (3, 4) are composed of one particular web of the bottom gusset material and two other webs of the bottom gusset material, the particular web of the bottom gusset material having a width two times as much as a width of the other webs of the bottom gusset material, the particular web of the bottom gusset material being supplied to the web of the first or second panel material (1, 2) and extended along longitudinal centerline thereof, the other webs of the bottom gusset material being supplied to the web of the first or second panel material (1, 2) and extend along opposite side edges thereof, the particular web of the bottom gusset material being slit along longitudinal centerline thereof after supplied, the webs of the first and second panel materials (1, 2) being also slit along the longitudinal centerline thereof before or after the particular and the other webs of the bottom gusset material (3, 4) are supplied, and the plastic bags being made two by two each of which includes the front and back surfaces formed by the webs of the first and second panel materials (1, 2), the one end surface formed by the particular web of the bottom gusset material and the other end surface formed by the other web of the bottom gusset material. a panel material feed device configured to superpose a web of a first panel material on a web of a second panel material and then feed the webs of the first and second panel materials (1, 2) longitudinally thereof; the apparatus being characterized by a first slit device configured to slit a plastic film along a longitudinal slit line so as to divide the plastic film into the web of the first panel material and a wide web of a bottom gusset material before the webs of first and second panel materials (1, 2) are superposed on each other, the webs of the first and second panel materials (1, 2) being superposed on each other and fed longitudinally after divided; a bottom gusset material feed device configured to feed the wide web of the bottom gusset material longitudinally after divided; a second slit device configured to further slit the wide web of the bottom gusset material so as to divide the wide web of the bottom gusset material into three webs of the bottom gusset material (3, 4); and a bottom gusset material guide device configured to guide and supply the three webs of the bottom gusset material (3, 4) to the web of the first or second panel material (1, 2), the bottom gusset material guide device being disposed a downstream side of the second slit device; wherein the three webs of the bottom gusset material (3, 4) are composed of one particular web of the bottom gusset material and two other webs of the bottom gusset material, the particular web of the bottom gusset material having a width two times as much as a width of the other webs of the bottom gusset material, the particular web of the bottom gusset material being supplied to the web of the first or second panel material (1, 2) and extended along longitudinal centerline thereof, the other webs of the bottom gusset material being supplied to the web of the first or second panel material (1, 2) and extend along opposite side edges thereof, the particular web of the bottom gusset material being slit along longitudinal centerline thereof after supplied, the webs of the first and second panel materials (1, 2) being also slit along the longitudinal centerline thereof before or after the particular and the other webs of the bottom gusset material (3, 4) are supplied, and the plastic bags being made two by two each of which includes the front and back surfaces formed by the webs of the first and second panel materials (1, 2), the one end surface formed by the particular web of the bottom gusset material and the other end surface formed by the other web of the bottom gusset material.