In a main metal piece 60 and an inner cylinder 70 serving as cylindrical bodies before welding, a second end surface 75 is an inclined surface that inclines toward an end portion opposite from the second end surface 75 as the second end surface 75 extends toward the center axis, and an angle θ2a is 5° to 15°. Thus, the distance between a first end surface 65 and the second end surface 75 positioned in resistance welding increases toward the center axis, and an angle θc (= angle θ2a) between the first end surface 65 and the second end surface 75 is 5° to 15°.