to the reactor 14 and a commutation circuit 32 comprising an auxiliary thyristor 26 an auxiliary reactor 28 and a capacitor 30 is provided for interrupting the flow of current through the thyristor 24 reactors 34 and 36 are connected in parallel with the reactor 14 these reactors 34 and 36 are respectively connected to dc power sources 38 and 40 similar to the dc power source 10 through switches 42 and 44 and thyristors 46 and 48 are respectively connected to the reactors 34 and 36 commutation circuits comprising auxiliary thyristors 50 52 auxiliary reactors 54 56 and capacitors 58 60 are respectively provided for interrupting the flow of current through these thyristors 46 and 48 another thyristor 66 and a pair of diodes 68 and 70 are connected between the reactor 14 and the respective reactors 34 and 36 the operation of the high voltage power supply device embodying the first form of the present invention having such a structure will be described with reference to fig1 and 2 in operation direct current is supplied to the reactor 14 from the dc power source 10 and a gate signal is applied to the gate of the thyristor 24 while the direct current is being supplied to the reactor 14 then when the power supply voltage of the dc power source 10 is reduced or the polarity thereof is inverted the current flowing from the dc power source 10 to the reactor 14 circulates now between the thyristor 24 and the reactor 14 the switch 12 is turned off at the time at which the current value flowing through the switch 12 is sufficiently decreased or reduced.