In a programmable power supply used in a semiconductor test apparatus, high-speed switching of a large current in a current rage or an output relay is enabled. In a MOSFET drive circuit 22 of a switch portion 20 provided in a programmable power supply 10 of a semiconductor test apparatus 1, a capacitor portion 22-12 is charged with electric charges by a current from a light receiving portion 22-12 of a light insulating element 22-1. When an SWA is turned on (SWB is turned off) by changeover of the analog switch portion 22-3, a gate of each MOSFET in the MOSFET portion 21 is charged with the electric charges stored in the capacitor portion 22-12, and enters an ON state. On the other hand, when the SWB of the analog switch portion 22-3 is turned on (SWA is turned off), the gate of the MOSFET is discharged.