Abstract: A dc power supply circuit connects a plurality of dc circuit breakers to a semi-conductor converter, returning again to the semi-conductor converter through a dc driving part such as an electric railcar connected to each dc circuit breaker. A second dc circuit breaker of larger capacity than the above-mentioned dc circuit breakers is provided in a return circuit and opened when a short circuit current is detected. A current decreasing means opens the second dc circuit breaker to decrease the short circuit current and includes, for example, a series-circuit of a resistor R and a reactor L. The dc power supply circuit has a large interruption capacity with low resistance loss.