A molded case circuit breaker, comprising: a case provided with a power side terminal portion and a load side terminal portion to which a power side external terminal and a load side external terminal are able to be connected, respectively; 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 portions (211, 212), 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 portions (211, 212); and an exhaustion cover mounted to the case with a structure to cover the exhaustion guiding portion, to thus block the arc gas passage, characterized in that the exhaustion cover is provided with sealing recesses (243, 244) therein and which sealing recesses (243, 244) are spaced from each other as seen in the gas discharge direction, and the exhaustion guiding portion is provided therein with sealing ribs (235, 236) protruding from the case and inserted into the sealing recesses (243, 244), wherein the sealing ribs (235, 236) include: first sealing ribs protruding from the case at an upstream side of the arc gas passage; and a second sealing rib protruding from the case at a downstream side of the arc gas passage, and wherein a land portion formed between the sealing recesses is engaged with the first sealing ribs. a case provided with a power side terminal portion and a load side terminal portion to which a power side external terminal and a load side external terminal are able to be connected, respectively; 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 portions (211, 212), 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 portions (211, 212); and an exhaustion cover mounted to the case with a structure to cover the exhaustion guiding portion, to thus block the arc gas passage, characterized in that the exhaustion cover is provided with sealing recesses (243, 244) therein and which sealing recesses (243, 244) are spaced from each other as seen in the gas discharge direction, and the exhaustion guiding portion is provided therein with sealing ribs (235, 236) protruding from the case and inserted into the sealing recesses (243, 244), wherein the sealing ribs (235, 236) include: first sealing ribs protruding from the case at an upstream side of the arc gas passage; and a second sealing rib protruding from the case at a downstream side of the arc gas passage, and wherein a land portion formed between the sealing recesses is engaged with the first sealing ribs. first sealing ribs protruding from the case at an upstream side of the arc gas passage; and a second sealing rib protruding from the case at a downstream side of the arc gas passage, and wherein a land portion formed between the sealing recesses is engaged with the first sealing ribs.