Circuit breaker

The circuit breaker (1) is provided with a mechanism unit (6) for opening/closing an electrical circuit, a command output unit (40) for outputting an operation command to operate the mechanism unit (6), a switch unit (15) operating upon completion of the operation of the mechanism unit based on the operation command, and an abnormality detection unit (16). The abnormality detection unit (16) detects an abnormality of the mechanism unit (6) on the basis of the difference between timing at which the operation command is output from the command output unit (40) and timing at which the switch unit (15) operates.