a circuit - breaking apparatus is formed of an insulating housing , first and second electrodes located at both ends of the insulating housing , a detonator located in the first electrode , a lead connected to the detonator for supplying an electric current to the detonator when the detonator is actuated , and a conductor disposed in the insulating housing . the conductor includes a fixed portion electrically connected to the first electrode , a circuit - breaking rod having narrow portions at both ends , and a barrel connected to the second electrode and having a cavity . the circuit - breaking rod is coupled to the fixed portion and the barrel through the narrow portions . the barrel has a locking section for locking in the cavity the circuit - breaking rod that has been shifted toward the second electrode due to cutoff of the narrow portions caused by the explosion of the detonator . accordingly , the circuit - breaking function is surely maintained , and it can be easily determined whether a circuit - breaking operation has been performed .