PURPOSE: To provide an ultrasonic welding machine for bonding cloths by a simple method.

CONSTITUTION: An ultrasonic generator which can move freely in the XY directions by means of an orthogonal-coordinates robot is moved down to the position for pressing a cloth A and a cloth B by an air cylinder 19 at the time of welding to radiate an ultrasonic wave at the position in which the cloths A and B are contacted closely to be welded. In order to prevent the dislocation of the cloths A and B, the cloths are spread on the surface of a base plate 3 in which a suction hole 5 is installed. A blower motor Mb is connected to the back of the base plate 3 through a pipe 12, and air is sucked from the front to the back of the base plate 3 by the blower motor Mb. In this way, the welding does not need thread to bond the cloths.