The invention discloses a circuit breaker for optimizing space allocation. The circuit breaker comprises a shell of which the width is two modulus values. A first overcurrent protection electrode of a single contact, a second overcurrent protection electrode of the single contact, components in the first overcurrent protection electrode of the single contact and the second overcurrent protection electrode of the single contact and an earth leakage protection device are arranged in the shell, wherein the first overcurrent protection electrode of the single contact contains a first handle, a first operating mechanism, a first short circuit instantaneous protection device, a first overload long time delay protection device, a first arc-extinguishing system, a test resistance and two first connecting terminals; the second overcurrent protection electrode of the single contact contains a second handle, a second operating mechanism, a second short circuit instantaneous protection device, a second overload long time delay protection device, a second arc-extinguishing system and two connecting terminals; the components in the first overcurrent protection electrode of a single contact and the second overcurrent protection electrode of the single contact are in symmetric mirror distribution; and the earth leakage protection device contains a mutual inductor, an electromagnetic trip, an electric leakage tripping mechanism, an electric leakage indicating mechanism and a test loop and is clamped between the first overcurrent protection electrode and the second overcurrent protection electrode in the width direction of the shell.