To provide a three-pole wiring breaker affecting no excessive load on a trip engagement part and capable of suppressing cost increase.

This three-pole wiring breaker having two trip engagement parts 12 and 22 is constructed by coupling a one-pole open/close tripping mechanism part 14 to a two-pole open/close tripping mechanism part 24 having a single trip engagement part so as to operate at the same time. As a concrete structure for coupling, the structure that couples a three-pole trigger lever, etc., can be adopted. Thereby, the three-pole wiring breaker affecting no excessive load on a trip engagement part and capable of suppressing cost increase can be attained.