In a method for manufacturing a terminal-equipped electrical wire a core wire of an electrical wire is connected to a flat plate-shaped electrical wire connector portion of a terminal. An ultrasonic welding jig including an anvil and a welding horn is provided. After the electrical wire connector portion is placed on the anvil, the core wire of the electrical wire is placed on the electrical wire connector portion. By applying ultrasonic vibration along the axial direction of the core wire while pressing the core wire using the welding horn, the core wire is ultrasonically welded to the electrical wire connector portion. On the upper surface of the wire connection portions of the terminal, a positioning groove, into which the core wire is fit, is formed in advance, and the core wire is placed on the electrical wire connector portion while being fit into the positioning groove.