PURPOSE: To prevent a lateral sealing location of films from slipping from a cut location, or prevent the slipping of a double sealing location, for which lateral sealing is continuously performed on films, or the slipping of a cut location from happening.

CONSTITUTION: A sensor 53 which detects a lateral sealing location of a film F is provided under a first lateral sealing unit. Also, a control means 54 which controls the driving speed of a second lateral heat-seal roll 11 or cutter unit 8 in response to the speed of the film F, based on a detecting signal from the sensor 53 is provided. The pattern of a detecting signal from the sensor 53 changes due to the speed variation of a lateral sealing location F2 under a transfer condition, and based on the variation of the detecting signal, the driving speed of the second lateral heat-seal roll 11 or cutter unit 8 is controlled to be adjusted to the transfer timing of the lateral sealing location F2 under a transfer condition.