When a movable blade cuts a distal end portion of a ground electrode member and is pulled back along a cut surface formed at a distal end of the ground electrode member, the distal end portion may move in the pull-back direction of the movable blade due to friction generated between the movable blade and the cut surface. This movement could cause deflective deformation of the ground electrode member. In order to restrain such movement, a support part is provided on the movable blade via a spring located near the cut surface. During the pull back step, the support part presses and supports the portion of the cut ground electrode member near the distal end thereof. Therefore, even when friction is generated when the movable blade is pulled back, the ground electrode member does not undergo deflective deformation.