Abstract: A film made of synthetic resin is pulled continuously from a roll thereof and formed into a tubular shape the overlapping longitudinal edge portions of which are fused. The interior of the resulting tubular film is filled with a liquid or viscous material to form a tubular body fed while it is being formed. The tubular body is squeezed intermittently at a predetermined time interval by a pair of rotating cylindrical rollers to form flattened portions devoid of the material, after which each flattened portion is constricted transversely of the tubular body to form a constricted portion. An ultrasonic horn and an anvil are brought into abutting contact with the constricted portion, which is sealed ultrasonically by holding the ultrasonic horn and anvil in abutting contact therewith at a constant contact pressure for a set period of time while the ultrasonic horn applies ultrasonic waves to the constricted portion.