PURPOSE: To use a battery effectively so as to prevent printing failure during a printing by a method wherein the printing is stopped temporarily when a battery voltage decreases below a fixed level during the printing and the printing is restarted after the battery voltage restores a level where the printing can be restarted.

CONSTITUTION: An unprintable level stored in a 1st memory means 2 is compared with a battery voltage level detected by a detector 1 at a 1st comparator 4. A print enable level stored in a 2nd memory means 3 is compared with the battery voltage level detected by the detector 1 at a 2nd comparator 5. When the battery voltage level is below the print enable level, it is repeated until a level above the print enable level is restored. When it is restored, the printing operation is restarted.