A piezoelectric-transformer high-voltage power supply in combination with an image-forming apparatus including a latent-image forming section configured to form an electrostatic latent image on an image carrier, a developing section configured to form a toner image on the electrostatic latent image, and a transfer section configured to transfer the toner image onto a transfer material includes a piezoelectric transformer; a piezoelectric-transformer drive circuit; an output-voltage setting-signal output circuit configured to output an output-voltage setting-signal; an output-voltage detector circuit, and a drive control circuit configured to output a control signal on the basis of a signal from the output-voltage detector circuit and the output-voltage setting-signal, for controlling the piezoelectric-transformer drive circuit. The output-voltage setting-signal output circuit outputs an output-voltage setting-signal corresponding to a voltage lower than a target voltage and, then, another output-voltage setting-signal corresponding to the target voltage.