To provide a high-voltage power source unit capable or restraining an overcurrent which is generated when a load is short-circuitted, even when a high-voltage power source is controlled digitally by a CPU.

A DC voltage Vin, supplied to the primary winding side of a step-up transformer 16, is subjected to switching by a switch element 20. An AC current, induced on the secondary winding side of the transformer 16, is rectified and smoothed by a rectifying and smoothing circuit 54 constituted of a diode 50 and a capacitor 52, and is supplied to a load through a resistor 72. The resistor 72 has a high impedance with a short-circuit current at most 100 μA, when the load is short-circuitted. When the total power is applied to the resistor 72 in an abnormal case that the load is short-circuitted, since a short-circuit current becomes smaller than or equal to 100 μA, the elements of the load and a high voltage power source part 12 with not be damaged.