PURPOSE: To make the driving intensity of a wire adjustable according to the number of sheets of paper to be printed by varying excited current of a head driving magnet in accordance with the changes in the gap between a printing head and a platen in an impact dot printer.

CONSTITUTION: When one sheet of paper is used, a knob is set to (a). The gap between the tip face of a printing head 11 and a platen 16 is reduced and a microswitch 19 is turned OFF. Under such a condition, when a driving signal is fed to an input terminal 39, a voltage of a battery 31 is supplied to a magnet coil 37 and the resultant excited current drives a wire in the printing head 11. When more than one sheets of paper are used, the knob is set to (b). With an aid of a projection 18, the microswitch is turned ON and the voltage of the battery 33 is supplied to the magnet coil 37 to drive the wire by a larger driving force than for one sheet of paper 21.