The utility model provides a circuit breaker and belongs to the technical field of low-voltage electrical apparatuses. The circuit breaker comprises a shell, an operation mechanism and a secondary connector, wherein the operation mechanism comprises a pair of side plates arranged in a parallel face-to-face mode; and the pair of side plates are fixedly arranged on the shell. The circuit breaker is characterized in that the top parts, in the height direction, of the pair of side plates respectively forms bending; and one end of the secondary connector is provided with a supporting frame forming fixed connection with the shell, and the other end of the secondary connector is provided with a supporting seat forming fixed connection with the bending on the pair of side plates. The circuit breaker has the advantages that force bearing of the secondary connector is balanced, the connection is more stable, the service life is improved, assembly and disassembly are convenient, and the operation is convenient.