A circuit breaker includes a main body case, an operating handle having a base portion and a knob portion protruding outwardly through a handle window frame opened in a cover of the main body case; a first shutter arranged between the base portion of the operating handle and the handle window frame, and disposed on the base portion, the first shutter being formed with a loose-fit hole to loosely fit the knob portion therethrough; and a second shutter disposed on the first shutter to move along with the knob portion. At ON and OFF positions of the operating handle, the first shutter extends beyond a front/rear edge of the handle window frame in a front-back direction to close the handle window frame, and the second shutter extends beyond a front/rear edge of the loose-fit hole in the front-back direction to close the loose-fit hole.