In an ultrasonic bonding method of an electric wire in which the electric wire 1 in which a conductor end 7 made of plural core wires is exposed and a metallic connection terminal 19 formed by erecting two side walls 27 from a bottom surface are prepared and the conductor end is bonded to the connection terminal by applying ultrasonic vibration while the conductor end of the electric wire is positioned in the bottom surface between the two side walls of the connection terminal and is pushed, a cross section of the conductor end of the electric wire is made by being molded by press so that a thickness of a width direction between the side walls becomes thin toward at least one of the side positioned in the bottom surface of the connection terminal and the side to which the ultrasonic vibration is applied.