A molded case circuit breaker comprising: a front space; a rear space divided from the front space; a fixed contact unit provided on one side of the front space and in electric contact with one of a power supply and a load; a movable contact unit installed in the front space to be movable and in contact with the fixed contact unit; a switching device installed in the rear space and operating to allow the movable contact unit to be in selective contact with the fixed contact unit; an operation device installed in the front space and the rear space and transferring the movable contact unit according to operation of the switching device; an arc extinguishment chamber installed on the one side of the front space and extinguishing an arc induced while the fixed contact unit is being separated from the movable contact unit; and a barrier preventing the arc from moving to the rear space, wherein the fixed contact unit includes a fixed pad, wherein the movable contact unit includes a movable portion and a contact pad which is fixed to the movable portion and is in selective contact with the fixed pad, wherein the barrier comprises: a lower barrier projection extended upwards from one side of a bottom surface of the front space; an upper barrier element provided on a top surface of the movable contact unit; and a lower barrier element provided on a bottom surface of the movable contact unit, and wherein, when the fixed pad and the contact pad are separated by a preset insulating distance, a position of the movable portion is designated as a circuit breaking position, characterized in that, the barrier further comprises an upper barrier projection extended downwards from one side of a top surface of the front space, wherein a bottom end of the upper barrier projection and a top end of the upper barrier element are located to be adjacent to each other in at least one position of the movable contact unit, wherein in said at least one position the movable contact unit is separated from the fixed contact unit, and wherein the movable portion is in contact with one side of the upper barrier projection while being located in the circuit breaking position. a front space; a rear space divided from the front space; a fixed contact unit provided on one side of the front space and in electric contact with one of a power supply and a load; a movable contact unit installed in the front space to be movable and in contact with the fixed contact unit; a switching device installed in the rear space and operating to allow the movable contact unit to be in selective contact with the fixed contact unit; an operation device installed in the front space and the rear space and transferring the movable contact unit according to operation of the switching device; an arc extinguishment chamber installed on the one side of the front space and extinguishing an arc induced while the fixed contact unit is being separated from the movable contact unit; and a barrier preventing the arc from moving to the rear space, a lower barrier projection extended upwards from one side of a bottom surface of the front space; an upper barrier element provided on a top surface of the movable contact unit; and a lower barrier element provided on a bottom surface of the movable contact unit, and