A circuit breaker for electric wiring according to the present invention includes: a lower case; an upper case which is combined with the upper end of the lower case; a main circuit unit which opens and closes a circuit by including a stationary contactor installed in the lower case and a movable contactor rotatable to a position of being in contact with or being separated from the stationary contactor; an opening and closing unit which is installed in the upper case and opens and closes the main circuit unit by being connected to the main circuit unit; and a mechanical tripping unit which is positioned in the upper case and triggers the opening and closing unit in order to operate to an opening driving position by being operated by absorption force when an abnormal current is generated in the main circuit unit. An insulating partition which is gradually and thickly formed along a part where the main circuit unit is positioned is included between the lower case and the upper case.
