Disclosed are a control unit for a circuit breaker capable of controlling and monitoring various types of switches such as a circuit breaker and a switchgear included in power system equipment, by being attached to the switches or by being implemented in the form of an independent module, and a controlling method thereof. The control unit for a circuit breaker, which interworks with a relay and a circuit breaker, includes: an Ethernet drive configured to receive a GOOSE message type control signal from the relay connected thereto through Ethernet communication; a control module configured to operate the circuit breaker based on the GOOSE message type control signal; and a main control unit (MCU) module configured to transmit the GOOSE message type control signal to the control module, if the received GOOSE message type control signal is related to the control unit.