PURPOSE:To enable to fusion-bond in a constant size adapted for fusion-bonding workpieces of the prescribed shape by stopping the drives of a motor and an oscillator when the content of a preset counter reaches the specific value and stopping the fusion-bonding operation. CONSTITUTION:Two thermoplastic resin sheets are interposed between a machining surface 11 and a press roller 12, the total feeding distance of workpieces is set in advance in a preset counter 19, a drive command signal S0 for outputting a start pulse P0 is outputted from an operation switch 14, and is applied to a feed controller 15 and an oscillation controller 16. A motor 8 is driven to rotate a machining horn 6, an oscillator 13 is driven to allow the horn 6 to vibrate in a supersonic frequency, and the workpieces are integrally heated and fusion-bonded. A position signal generator 18 continuously detects the rotating speed of the motor 8 and outputs a rotation signal Sn responsive to the feeding distance of the workpieces, thereby gradually decreasing the counted content of the counter 19. When the counted content eventually becomes the specific value, a stop command signal SP is outputted to stop the drives of the motor 8 and the oscillator 18, thereby stopping the fusion-bonding operation.