Disclosed is a mold cased circuit breaker (MCCB) comprising a plurality of single pole breaking units simultaneously opened and closed by a pair of common shaft pins. The MCCB effectively transmits a torque for opening or closing contacts to adjacent single pole breaking unit for electrical pole with a minimized loss, and prevents the shaft pins from being bent. The MCCB comprises a crank installed across the pair of shaft pins so as to connect the shaft pins to each other.