To make it possible to eliminate the need for preheating, to dispense with smaller electric power consumption and to prevent an operator from incurring a bun.

This apparatus welds belt-like powder paper 2 transporting in the extending direction of folds. The apparatus has an ultrasonic welding means 3 which is made freely movable in the direction orthogonal with the direction described above along the surface 30 of the powder paper 2 and ultrasonically welds the powder paper 2. This ultrasonic welding means 3 is provided with an ultrasonic vibration transmission section 4 for transmitting ultrasonic vibration and a receiving jig 5 which holds the powder paper 2 between the ultrasonic vibration transmission section 4. This receiving jig 5 has a weld forming section 16 for welding the powder paper 2. The weld forming section 16 extends its apexes 19 in an orthogonal direction with the cross-sectional contours of curved shapes projecting as the contact parts with the powder paper. The rugged parts 63 are formed at the apexes 19.