PURPOSE: To provide the power supply circuit for bar code scanner which is improved in utilizing efficiency of a battery power source, prolongs the service life of the battery power source and is not affected by an amt. of internal voltage drop or load state.

CONSTITUTION: This circuit is provided with a DC/DC converter 8 to generate a boosting voltage from the output voltage of a battery power source 9, first input terminal 11 to receive the output voltage of the battery power source 9, second input terminal I2 to receive the boosting voltage and voltage adjusting circuit 1 equipped with an output terminal O to selectively output either a first voltage equal to the operating voltage of a load device such as a CCD line sensor for bar code reader, for example, or a second voltage a little lower than the operating voltage. Further, the voltage adjusting circuit 1 is composed of 1st and 2nd voltage adjusters 2 and 3 to generate the first and second voltages, voltage detector 4 to detect the voltage of the output terminal O, and switching part 5 to be closed by the detection output.