| 摘要 |
PROBLEM TO BE SOLVED: To hold a printing quality constant irrespective of a battery or an external power source as a power supply source. SOLUTION: In the portable printer for printing by a thermal head driven by a power from either a battery or an external power source, a driving voltage is measured (step S2), which power of the battery and the external power source is supplied is decided by the measured value (steps S3 to S5), a printing operation is differentiated in response to the decided result (steps S7 to S9), thereby control conditions adapted to the battery and the power source having a difference at an obtained voltage value can be selected, and hence stable printing quality can be obtained.
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