A circuit breaker (100) having a circuit operating device (400) according to one embodiment of the present invention includes a circuit unit (110) having a main circuit, a detecting unit (120) havinga detection circuit for detecting a fault current in the main circuit, and the circuit operating device (400) configured to allow connection or isolation between the main circuit and the detection circuit, wherein the circuit operating device includes a first fixed unit (430) and a second fixed unit (450) connected to the main circuit and the detection circuit, respectively, and arranged in parallel to each other, and a moving unit (410) rotatably coupled between the first fixed unit and the second fixed unit to connect or isolate the main circuit and the detection circuit to or from each other.