PURPOSE: To easily improve equivalency of a recovering voltage for a direct test by providing a reactor obtaining the recovering voltage of a resonance frequency conformed with a system frequency and a changeover switch.

CONSTITUTION: The changeover switch 13 is provided between the reactor 9 and a circuit breaker 6 to be tested. When an interruption is made by the circuit breaker 6, a triggertron gap 8 is ignited and the regenerating voltage is impressed on the breaker 6 from a capacitor 7 through the reactor 9. At the time when this oscillation is over (1-2ms after the interruption is finished), the SW 13 is changed over to the reactor 14 side. A resonance voltage between the reactor 14, capacitors 11, 12 and resistor 10 is thereby impressed on the breaker 6. For the waveform of transient recovering voltage, a voltage having the oscillating frequency and amplitude factor as the regenerating voltage is impressed until the changed over timing t1 of the SW 13, and after the timing t1 an oscillating voltage of the system frequency according to the reactor 14 and the capacitor 11 is impressed, then the recovering voltage equivalent to that of the direct test can be impressed.