PURPOSE: To eliminate releasing of a bag by a hand operation after molding by continuously connecting a zipper member to a dressing material and molding the member in a state disconnected from its engagement.

CONSTITUTION: A dressing material 2 is fed in a superposed state, supplied in a direction of an arrow A by rotating feed rollers 3, and molded to a bag. Here, it is inserted to a part of the material corresponding to a port of the bag in a state that a male piece 1b is engaged with a female piece 1a. A connecting block 4 made of a heater is pressed from above and below to a port pat of the material 2 inserted with a zipper member 1. Thus, the member 1 is connected to an inner surface of the material 2. A separating lip 5 separates the member 1 of an engaged state thereby to continuously release the port of the material 2. Then, a horn 6 of an ultrasonic fastening unit at a downstream side of the lip 5 is vertically moved to operate an ultrasonic vibration at the member 1 at each predetermined interval, thereby fusion-bonding to seal the member 1.