The invention provides a switching circuit and a power converter having a built-in power source for a conduction control terminal even if they have a single-arm structure. In the switching circuit having a switching device and a conduction control terminal power source capacitor, a negative terminal of the capacitor is connected to a reference voltage terminal of a main power source and to the gate terminal selectively through a half-bridge circuit and a positive terminal of the capacitor is selectively connected to a positive terminal of the main power source and to a source terminal of the switching device through a half-bridge circuit. The capacitor is charged when the positive terminal is connected to the main power source and discharges when the negative terminal is connected to the gate terminal and the positive terminal is connected to the source terminal and applies voltage to the gate terminal of the switching device.