To prevent changing of a lug length and damaging of the sense of beauty by automatically adjusting cutting positions without stopping bag making work when positions of marks printed on a bag making continuous film are changed.

A bag making device comprises a sensor 6 for sensing marks, a sealing device 3 for sealing bag bottom sections, a roller feed device 2 for feeding and stopping a film 1, a cutting device 4 for cutting the film 1 on the downstream side of the roller feed device and a cutting position adjusting device 8 forming a detour between the sealing device 3 and the roller transfer device 2 and freely adjusting the length of the detour. When the mark pitch of the film 1 is changed and the number of pulses transmitted by an encorder device 2c is changed, an adjustment motor 8b is rotated in compliance with the amount of changes to change the position of the adjustment roller and also adjust the length of the detour.