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 (201H, 201L) 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 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 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 (201H, 201L) 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 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 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 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 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 connected to the second rectifier circuit.