Disclosed is a display device for a thermal magnetic type molded case circuit breaker capable to display a phase deficiency occurred on a line to a user such that the user rapidly deals with the phase deficiency and prevents loss caused by over-heating generated due to the phase deficiency. The thermal magnetic type molded case circuit breaker has a bimetal, which is bendable when heat is applied thereto, and a shifter coupled to an upper end of the bimetal and horizontally moved corresponding to a bending degree of the bimetal when over-current is applied thereto. The display device includes a power source for supplying electric power, a display for displaying the phase deficiency of the thermal magnetic type molded case circuit breaker by receiving power from the power source, a stationary contactor electrically connected to the power source and having a stationary contact, and a movable contactor electrically connected to the display and having a movable contact. The movable contactor vertically moves and forms a circuit together with the power source section and the display for displaying the phase deficiency state when the movable contact contacts with the stationary contact. A interlock lever rotates according to a horizontal movement of the shifter. A connection bar makes contact with both shifter and interlock lever so as to transfer horizontal moving force of the shifter to the interlock lever. A latch lever is installed adjacent to the interlock lever in order to restrict a movement of the movable contactor when normal current is applied and to release a restriction of the movable contactor when the phase deficiency occurs.