A main reference value setting unit generates a voltage reference value DREF—V which represents a target level of a power supply voltage VDD. A digital calculation unit generates a main control value DOUT by digital calculation such that a digital voltage measurement value DM—V which represents the voltage level of the current power supply voltage VDD matches the voltage reference value DREF—V. A main D/A converter converts the main control value DOUT into an analog power supply signal SPS, and supplies the analog power supply signal SPS thus generated to a power supply terminal of a DUT via a power supply line. An auxiliary current source supplies an auxiliary current ISUB to the power supply terminal of the DUT via a sub-path that differs from the power supply line.