In order to realize a stable rocking operation of the armature for performing high-speed printing, between the armature spacer for accommodating and holding the support shaft of the armature which supports the printing wires, and the yoke for holding the support shafts of the plurality of armatures together with this armature spacer, there is provided the abrasion preventing member formed of material having higher magnetic permeability than that of the yoke, and hardened by surface hardening processing.