Changes in the form of a pressure welding part of a bonding tool for ultrasonic bonding due to abrasion of the pressure welding part and/or accumulation of foreign matter, such as plating material, on the pressure welding part during use of the bonding tool are prevented, so that the bonding tool can carry out ultrasonic bonding stably. A plurality of protrusions with curved outer surfaces are formed on the pressure welding part that contacts the bonded part during ultrasonic bonding. The protrusions can be formed with spherical outer surfaces by forming concave grooves in a grid in an end surface of the bonding tool and then sandblasting the end surface of the bonding tool.