A circuit breaker having a circuit operating device according to one embodiment of the present invention includes a circuit unit having a main circuit, a detecting unit having a detection circuit for detecting a fault current in the main circuit, and a circuit operating device configured to allow connection or isolation between the main circuit and the detection circuit, wherein the circuit operating device includes a first fixed unit and a second fixed unit connected to the main circuit and the detection circuit, respectively, and arranged in parallel to each other, and a moving unit 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.