Abstract: Disclosed is a high speed automatic circuit breaker in which a Rogowski coil is integrated with a voltage sensor, a microprocessor processes voltage and current signals through an electronic transformer to reduce a size and costs, and an algorithm of counting, charging, and trip is realized for coordination with reclosers of a power substation and a line. The circuit breaker includes a main body to receive an electric power when fixed and moving contacts contacting each other, to operate the moving contact using an trip coil according to a trip control signal to trip, and to input the electric power according to an closing control signal, and a control unit to monitor current of a lead-in line and voltage to generate a control signal of controlling the main body. Thus, costs and installing space can be reduced and a customer fault is fundamentally prevented from being propagated to the line.