6 output by the cpu 30 is negated in a low level next the printing power supply switch signal output from the output terminal for switch 30 a of the cpu 30 is switched to low to carry currents through the resistors r 4 r 5 to turn on the transistor tr 1 therefore a printing power supply 20 a applies a voltage to the thermal head 1 the cpu 30 measures the voltage appeared in the analog input terminal for voltage measurement 30 b in order to measure the voltage applied to the thermal head 1 in this case since the voltage of the printing power supply 20 a is divided by the fixed resistors r 1 r 2 of a predetermined ratio of resistance when the voltage to be input into the analog input terminal for voltage measurement 30 b is measured the voltage of the printing power supply 20 a can be obtained the voltage measured by the above described procedure is compared with the rated voltage of the thermal head consisting the thermal head property data stored in the above described rom 33 thereby making it as one standard for the model determination of the printer engine pe next the constitution of the head configuration measuring circuit 35 will be described the.