Disclosed is a molded case circuit breaker. The molded case circuit breaker includes a case; an interrupter assembly installed in the case, and provided with an arc gas outlet for discharging arc gas generated from inside of the interrupter assembly to outside; an exhaustion guiding portion disposed between the interrupter assembly and the terminal portion, and provided with a discharge chamber therein, to thus provide an arc gas passage between the arc gas outlet and a vent chute of the terminal portion; and an exhaustion cover mounted to the case with a structure to cover the exhaustion guiding portion, to thus block the arc gas passage.