In a filter circuit with a low-pass filter, the output of the low-pass filter is regenerated over a reverse current diode with the input of the low-pass filter or of a further low-pass filter pre-connected to the low-pass filter. The heating unit has a medium passage through which the recording medium after printing passes, a heating unit provided with a heat generator disposed in an intermediate position of the medium passage to heat the recording medium after printing with heat generated by the heat generator, and an air discharging unit for forcibly discharging air in the medium passage. A backup process pair is established for the primary pair and information is transferred thereto so that it can take over for the primary pair should that pair fail. Each output of the shift register is coupled to one pin of the corresponding pin segment. An alternative use of known locks for key operation or handle operation is not possible.