An air circuit breaker comprising a delay time generation apparatus for outputting a conductive signal through a switch with a preset delay time when a movable contactor is brought into contact with a fixed contactor, the apparatus comprising: a pin portion moved downward when the movable contactor is brought into contact with the fixed contactor; a main shaft rotated in response to a movement of the movable contactor to a contact position or a trip position; a first rotating unit located to be closely adhered on the main shaft, the first rotating unit being rotated in a clockwise direction through the pin portion when the movable contactor is moved to the contact position, and rotated in a counterclockwise direction through the main shaft when the movable contactor is moved to the trip position; and a second rotating unit located below the first rotating unit, the second rotating unit being rotated in response to the rotation of the first rotating unit to be brought into contact with or separated from the switch such that the conductive signal is output, wherein the first rotating unit comprises: a body portion having connection arms extending from both sides thereof in a bent manner to be connected to an inside of the air circuit breaker; a holder located between the connection arms and pushed down by the pin portion when the movable contactor is moved to the contact position; characterized in that the first rotating unit is released from the adhered state on the main shaft when the movable contactor is moved to the contact position, the holder is provided with a protrusion protruding upwardly from an upper end, the outer peripheral surface of the protrusion being formed in a rounded shape, and the pin portion is provided with a pressing plate disposed on the outer peripheral surface thereof to press the protrusion in response to a movement of the pin portion. a pin portion moved downward when the movable contactor is brought into contact with the fixed contactor; a main shaft rotated in response to a movement of the movable contactor to a contact position or a trip position; a first rotating unit located to be closely adhered on the main shaft, the first rotating unit being rotated in a clockwise direction through the pin portion when the movable contactor is moved to the contact position, and rotated in a counterclockwise direction through the main shaft when the movable contactor is moved to the trip position; and a second rotating unit located below the first rotating unit, the second rotating unit being rotated in response to the rotation of the first rotating unit to be brought into contact with or separated from the switch such that the conductive signal is output, wherein the first rotating unit comprises: a body portion having connection arms extending from both sides thereof in a bent manner to be connected to an inside of the air circuit breaker; a holder located between the connection arms and pushed down by the pin portion when the movable contactor is moved to the contact position; characterized in that a body portion having connection arms extending from both sides thereof in a bent manner to be connected to an inside of the air circuit breaker; a holder located between the connection arms and pushed down by the pin portion when the movable contactor is moved to the contact position; characterized in that