A switching element , comprising: a first terminal and a second terminal which are used in configuring a serial switching element group by being built in a power converter (102a-102d) for electrically converting a grid current, the grid current being an alternate current, into a direct current or electrically converting a direct current into an alternate current; energy accumulation means ; a plurality of controllable switches that are controllable to enable outputting of accumulated energy accumulated by the energy accumulation means , the accumulated energy being output between the first terminal and the second terminal ; and an internal power source for supplying power to the switching element itself, using a current flowing in a portion of the power converter (102a-102d); characterized in that : the internal power source comprises: a first rectifier circuit that obtains a current flowing through the first terminal and the second terminal by a current transformer and rectifies the current; and a first capacitor (C1) connected to the first rectifier circuit ; and the internal power source further comprises: a second rectifier circuit that obtains a voltage applied between the first terminal and the second terminal and rectifies the voltage; and a second capacitor (C2) connected to the second rectifier circuit . a first terminal and a second terminal which are used in configuring a serial switching element group by being built in a power converter (102a-102d) for electrically converting a grid current, the grid current being an alternate current, into a direct current or electrically converting a direct current into an alternate current; energy accumulation means ; a plurality of controllable switches that are controllable to enable outputting of accumulated energy accumulated by the energy accumulation means , the accumulated energy being output between the first terminal and the second terminal ; and an internal power source for supplying power to the switching element itself, using a current flowing in a portion of the power converter (102a-102d); characterized in that : the internal power source comprises: a first rectifier circuit that obtains a current flowing through the first terminal and the second terminal by a current transformer and rectifies the current; and a first capacitor (C1) connected to the first rectifier circuit ; and the internal power source further comprises: a second rectifier circuit that obtains a voltage applied between the first terminal and the second terminal and rectifies the voltage; and a second capacitor (C2) connected to the second rectifier circuit . a first rectifier circuit that obtains a current flowing through the first terminal and the second terminal by a current transformer and rectifies the current; and a first capacitor (C1) connected to the first rectifier circuit ; and the internal power source further comprises: a second rectifier circuit that obtains a voltage applied between the first terminal and the second terminal and rectifies the voltage; and a second capacitor (C2) connected to the second rectifier circuit . a second rectifier circuit that obtains a voltage applied between the first terminal and the second terminal and rectifies the voltage; and a second capacitor (C2) connected to the second rectifier circuit . <EOS>