A yoke lever (23) comprises an upper wall (23a), and a pair of side walls (23b) which extend downward from both side portions in a width direction which is orthogonal to a longitudinal direction of the upper wall (23a). A long hole (23d) is formed in the upper wall (23a), and a rotation connection target portion (23e) is formed on the side wall (23b). A secondary lever (22) comprises an insertion connection portion (22b) which extends downward from a longitudinal end thereof and is assembled with the long hole (23d) by being inserted therein from above. The insertion connection portion (22b) comprises an insertion cylindrical portion (22e) which is configured from a pair of opposing side walls (22c) opposing an inner side surface of the side wall (23b) of the yoke lever (23), and a pair of end walls (22d) connecting longitudinal ends of the opposing side walls (22c) with each other. The insertion cylindrical portion has an approximately rectangular cylindrical shape when seen from below, which is long in a longitudinal direction, and a rotation connection portion (22f) which projects from a longitudinal center of the opposing side wall (22c) is engaged with the rotation connection target portion (23e) in a rotatable manner.