The invention acquires a circuit breaker which does not give rise to fusion even if lightning surge invades, and a SPD protection system using the circuit breaker. In the invention, the circuit breaker is configured on the upstream of the SPD and located in the circuit branched from the bus, the SPD is configured between an input side of a load apparatus connected to the bus and the ground; the circuit breaker is composed of: a shell; a switch unit which is contained in the shell to make and break the current flowing through the circuit; a current tripping element which follows up when the current is the surge current generated by the lightning; and a crank connecting rod which enables the switch unit to operate on the basis of the operations of the current tripping element so as to breakthe circuit, when the surge current gets through the circuit breaker, the current tripping element is operated to break the circuit before the electric arc, on account of the surge current, is generated between an immovable contact and a movable contact that form the switch unit.