The present invention enables a core wire that contains a plurality of strands and a bonding object to be bonded more reliably using an ultrasonic bonding device that cantilever supports a pressing portion that performs ultrasonic bonding. A bonding object (for example, a terminal) is supported as on a stage, a core wire is overlaid on the bonding object, and the core wire and the bonding object are ultrasonically bonded in a state where the core wire is pressed toward the bonding object, using a pressing portion that is supported in cantilever fashion. During ultrasonic bonding, a pressing surface of the pressing portion is inclined in a pressing direction progressively toward a side where the pressing portion is cantilever supported, and also a bonding surface of the bonding object is inclined in the pressing direction progressively toward the side where the pressing portion is cantilever supported.