A bag making apparatus for successively making bags from a continuous sheet panel and a continuous strip member, the bag making apparatus comprising: a feed device configured to intermittently feed the sheet panel and the strip member in a longitudinal direction of the sheet panel and the strip member; a welding device configured to weld the sheet panel and the strip member to each other in a zone where the sheet panel is intermittently fed by the feed device; and a cut device disposed downstream of the welding device and configured to cross-cut the sheet panel and the strip member in a width direction of the sheet panel during every intermittent feed cycle, the welding device comprising: a pressure unit comprising a pair of pressure rollers for pressurizing the sheet panel and the strip member superposed on each other during a feed phase of an intermittent feed cycle; and a laser unit configured to irradiate the sheet panel or the strip member with a laser beam at an irradiation position spaced upstream away from a pressure position (P 0) of the pressure unit to melt the sheet panel or the strip member using the laser beam, wherein a part of the sheet panel or the strip member irradiated with the laser beam returns to a non-molten state due to decrease in temperature in a section from the irradiation position to the pressure position (P 0) during a pause phase of an intermittent feed cycle, so that an unwelded part is generated every intermittent feed cycle, the bag making apparatus further comprising: a movement device for moving the pressure unit and the laser unit together upstream and downstream while maintaining a relative positional relationship between the pressure position (P 0) and the irradiation position; and a control device configured to control the movement device to move the pressure unit and the laser unit together upstream and downstream during a pause phase of an intermittent feed cycle, thereby adjusting a position on the sheet panel where the unwelded part is generated, in the longitudinal direction of the sheet panel. a feed device configured to intermittently feed the sheet panel and the strip member in a longitudinal direction of the sheet panel and the strip member; a welding device configured to weld the sheet panel and the strip member to each other in a zone where the sheet panel is intermittently fed by the feed device; and a cut device disposed downstream of the welding device and configured to cross-cut the sheet panel and the strip member in a width direction of the sheet panel during every intermittent feed cycle, the welding device comprising: a pressure unit comprising a pair of pressure rollers for pressurizing the sheet panel and the strip member superposed on each other during a feed phase of an intermittent feed cycle; and a laser unit configured to irradiate the sheet panel or the strip member with a laser beam at an irradiation position spaced upstream away from a pressure position (P 0) of the pressure unit to melt the sheet panel or the strip member using the laser beam, a pressure unit comprising a pair of pressure rollers for pressurizing the sheet panel and the strip member superposed on each other during a feed phase of an intermittent feed cycle; and a laser unit configured to irradiate the sheet panel or the strip member with a laser beam at an irradiation position spaced upstream away from a pressure position (P 0) of the pressure unit to melt the sheet panel or the strip member using the laser beam, wherein a part of the sheet panel or the strip member irradiated with the laser beam returns to a non-molten state due to decrease in temperature in a section from the irradiation position to the pressure position (P 0) during a pause phase of an intermittent feed cycle, so that an unwelded part is generated every intermittent feed cycle, the bag making apparatus further comprising: a movement device for moving the pressure unit and the laser unit together upstream and downstream while maintaining a relative positional relationship between the pressure position (P 0) and the irradiation position; and a control device configured to control the movement device to move the pressure unit and the laser unit together upstream and downstream during a pause phase of an intermittent feed cycle, thereby adjusting a position on the sheet panel where the unwelded part is generated, in the longitudinal direction of the sheet panel. a movement device for moving the pressure unit and the laser unit together upstream and downstream while maintaining a relative positional relationship between the pressure position (P 0) and the irradiation position; and a control device configured to control the movement device to move the pressure unit and the laser unit together upstream and downstream during a pause phase of an intermittent feed cycle, thereby adjusting a position on the sheet panel where the unwelded part is generated, in the longitudinal direction of the sheet panel.