PURPOSE: To simply and inexpensively embody the adjustment at the time of the production of a voltage detection means at a high speed with a high accuracy when the voltage of the driving power supply of a printer mechanism or a printing head is controlled while monitoring.

CONSTITUTION: The test program ROM 107 stored in the outside of a printer and used at the time of adjustment and a program changeover means 131 detecting the test program ROM 107 is connected by a connection means 122 to transfer control to the test program ROM 107 are mounted. Further, a voltage correction table forming program forming a data conversion table for correcting a voltage measured value when the power supply of the printer is turned ON and a voltage correcting program obtaining the voltage value corrected by subtracting the data conversion table from the output value of an A/D converter 102 in voltage detecting timing are provided.