A power-supply circuit for supplying voltage to a load while freely selecting positive voltage and negative voltage using a single power supply has a power supply that generates power-supply voltage, an inverted outputting circuit having a positive voltage terminal for outputting positive voltage based on the power-supply voltage and a negative voltage terminal for outputting negative voltage generated based on the power-supply voltage and having different polarity from the positive voltage and outputting the positive and negative voltage while keeping the same direction in terms of directions of electric current flowing between the positive voltage terminal and the outside and of electric current flowing between the negative voltage terminal and the outside and a step-down output circuit for supplying predetermined voltage to the load by connecting the positive voltage terminal and the negative voltage terminal to the load while switching them with a predetermined duty ratio.