To provide an uniterruptive testing device capable of carrying out an overcurrent circuit breaker functional test for a wiring circuit breaker while the wiring circuit breaker is connected with a main circuit.

The uninterruptive testing device 10 is provided with a low voltage large current insulation type power source 13 supplying a DC testing current to a wiring circuit breaker and moreover insulated from a main circuit, a voltage detecting part 15 provided with a low impedance element arranged at an output side of the low voltage large current insulation type power source 13 and arranged in parallel with the low voltage large current insulation type power source 13 and detecting a voltage generated on either end of the low impedance element by a flow of the DC testing current to the low impedance element, when a main circuit contact of the wiring circuit breaker is shut down by the DC testing current, a first to a third switching units 141a, 141b, 142, 143 functioning as electrical cutting-off means of the low voltage large current insulation type power source 13 from the wiring circuit breaker, when the voltage value of the voltage detected by the voltage detecting part 15 is a given value or higher, and a controlling part 16.