A DC circuit breaker device comprising: - a first semiconductor switch and a second semiconductor switch connected in series between a first node on a main circuit line and a second node on the main circuit line such that current-carrying directions of the switches are opposite to each other; - a first diode connected in parallel with the first semiconductor switch to carry a current in a direction opposite to the current-carrying direction of the first semiconductor switch; - a second diode connected in parallel with the second semiconductor switch to carry a current in a direction opposite to the current-carrying direction of the second semiconductor switch; and - a first mechanical circuit breaker; and characterized by further comprising: - a second mechanical circuit breaker; the first mechanical circuit breaker and the second mechanical circuit breaker successively connected in series between the first node and the second node, and connected in parallel with the whole of the first semiconductor switch and the second semiconductor switch; - a first backward current generation circuit and a second backward current generation circuit successively connected in series between the first node and the second node, and connected in parallel with the whole of the first semiconductor switch and the second semiconductor switch and in parallel with the whole of the first mechanical circuit breaker and the second mechanical circuit breaker, to pass a backward current through the first mechanical circuit breaker and the second mechanical circuit breaker, respectively; - an injection switch connected between a third node between the first mechanical circuit breaker and the second mechanical circuit breaker and a fourth node between the first backward current generation circuit and the second backward current generation circuit; and - a controller adapted to control timing of opening/closing the first semiconductor switch, the second semiconductor switch, the first mechanical circuit breaker, the second mechanical circuit breaker, and the injection switch. - a first semiconductor switch and a second semiconductor switch connected in series between a first node on a main circuit line and a second node on the main circuit line such that current-carrying directions of the switches are opposite to each other; - a first diode connected in parallel with the first semiconductor switch to carry a current in a direction opposite to the current-carrying direction of the first semiconductor switch; - a second diode connected in parallel with the second semiconductor switch to carry a current in a direction opposite to the current-carrying direction of the second semiconductor switch; and - a first mechanical circuit breaker; and - a second mechanical circuit breaker; the first mechanical circuit breaker and the second mechanical circuit breaker successively connected in series between the first node and the second node, and connected in parallel with the whole of the first semiconductor switch and the second semiconductor switch; - a first backward current generation circuit and a second backward current generation circuit successively connected in series between the first node and the second node, and connected in parallel with the whole of the first semiconductor switch and the second semiconductor switch and in parallel with the whole of the first mechanical circuit breaker and the second mechanical circuit breaker, to pass a backward current through the first mechanical circuit breaker and the second mechanical circuit breaker, respectively; - an injection switch connected between a third node between the first mechanical circuit breaker and the second mechanical circuit breaker and a fourth node between the first backward current generation circuit and the second backward current generation circuit; and - a controller adapted to control timing of opening/closing the first semiconductor switch, the second semiconductor switch, the first mechanical circuit breaker, the second mechanical circuit breaker, and the injection switch.