The invention discloses a circuit breaker, which can prevent unnecessary operations caused by start inrush current and start current. The circuit breaker (1) comprises a bypass circuit that has a second double-metal member (29) which can be in touch with or separated from a load side terminal (6); the second double-metal member (29) moves in the following way: if the circuit breaker (1) is switched on or the power of a motor is on, the second double-metal member (29) is in contact with a contact part (6a) of the load side terminal (6) and is in parallel with a trip device (2) for the current flow; if a preset temperature is reached, the second double-metal member (29) is separated from the load side terminal (6), and the current only flows in the trip device (2).