断路器（英语：Circuit Breaker，简称CB），又称为遮断器，而香港称为水气掣或漏电断路器，为一种过电流保护之设备，可使用于室内配在线使用之总开关与分电流控制开关（ON/OFF POWER），亦可有效的保护电器的重要组件，主要用作短路保护和防止严重超载，工业机器上的马达负载保护也会指定使用断路器做为保护设备之一。

在低压用断路器，最常见为无熔丝开关，较大型容量之低压断路器最常见的是空气断路器（Air Circuit Breaker，缩写ACB）。

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overcurrent or overload or short circuit. Its basic function is to interrupt current flow after protective relays detect a fault. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city. The generic function of a circuit breaker, RCD or a fuse, as an automatic means of removing power from a faulty system is often abbreviated to ADS (Automatic Disconnection of Supply).