To provide a circuit breaker which can rapidly discharge high-temperature gas generated in short-circuit break from the vicinity of a contact to an outside of a body, and a distribution board using the circuit breaker.

The circuit breaker 10 includes: a body 11 structured of an electrically-insulating case body 11a; a power supply connection part 12 arranged on one side of the body; a load connection part 13 arranged on other side of the body; a movable contact plate 14 housed in the body and connected to the power supply connection part; a fixed contact plate 15 housed in the body so as to face the movable contact plate, connected to the load connection part, having an opening part 15b formed by passing through a terminal plate 15a, and including a fixed contact 15c biased in a direction of the opening part; and a circuit breaking part 16 for opening/closing connection between the movable contact plate and fixed contact plate.