To accomplish both prevention of disengagement of the shoe-hold spring from the shoe-hold apparatus and improvement of the assemblability of the same. The shoe-hold pin has the small diameter portion and the large diameter portion. One end opened slots are formed at the pair of arms of the U-shaped shoe-hold spring, and the slots are such that the small diameter portion of the shoe-hold pin is passable therethrough and the large diameter portion is non-passable.The pin-insertion hole, which is continuous to the slot of the web side arm and may position the large diameter portion therein, is formed in the web side arm and restricts the shoe-hold spring from disengaging therefrom when the large diameter portion of the shoe-hold pin is positioned in the pin-insertion hole.