In a case for a circuit breaker in which a terminal is simply replaceable or mountable according to a wiring method of the circuit breaker, the case comprises a case which accommodates components for breaking a circuit, a terminal block portion which provides a common platform for plural types of terminals, and a door engaged with the case in monolithic form so that it may be operable to a closed position for closing the case or an opened position for installing a selected terminal of the plural types of terminals.