PURPOSE: To enable smooth starting of a magnet, by flowing current of a frequency where the magnet does not respond in a coil while the magnet is inoperative.

CONSTITUTION: High-frequency current i flows in a coil 2 for a time T1 and a period T2, while a wire dot printer stops print-driving. The time and perid are determined by thermal quantity produced at an inoperative frequency of a magnet. Then, a core 1 is warmed by heat produced within the coil 2 and by eddy current in the core 1. Oil film in the contact surface between the core 1 and an armature 3 gets hot and decreases in viscosity. Such a status enables smooth starting, when a printing magnet 21a starts at a normal drive current. The starting will be made possible in a short time during a cold season on the condition that weak current i flows in the coil 2 of printing magnet 21a for the time T1 and peroid T2 as soon as the wire dot printer is powered ON.