A miniature circuit breaker, comprising a housing defining an interior space; a control circuit board, disposed in the interior space; an operating mechanism comprising a handle, a latch connected to the handle, a trip bar capable of being locked with or unlocked from the latch, and a contact support frame supporting the latch and the trip bar; a first phase circuit comprising a first wiring terminal, a first stationary contact electrically connected to the first wiring terminal, a first movable contact pivotally connected to the contact support frame, and a second wiring terminal; a second phase circuit comprising a third wiring terminal, a second stationary contact electrically connected to the third wiring terminal, a second movable contact pivotally connected to the contact support frame, and a fourth wiring terminal electrically connected to the second movable contact; a closing actuating mechanism, electrically connected to the control circuit board and connected to and driving the operating mechanism; a first current detection device, configured to detect a current flowing through the first stationary contact, and electrically connected to the control circuit board; a second current detection device, configured to detect a current flowing through the second wiring terminal and the fourth wiring terminal, and electrically connected to the control circuit board; and an opening actuating mechanism, electrically connected to the second wiring terminal and the control circuit board, and configured to selectively drive the trip bar to be unlocked from the latch based on current information detected by the first current detection device and the second current detection device. a housing defining an interior space; a control circuit board, disposed in the interior space; an operating mechanism comprising a handle, a latch connected to the handle, a trip bar capable of being locked with or unlocked from the latch, and a contact support frame supporting the latch and the trip bar; a first phase circuit comprising a first wiring terminal, a first stationary contact electrically connected to the first wiring terminal, a first movable contact pivotally connected to the contact support frame, and a second wiring terminal; a second phase circuit comprising a third wiring terminal, a second stationary contact electrically connected to the third wiring terminal, a second movable contact pivotally connected to the contact support frame, and a fourth wiring terminal electrically connected to the second movable contact; a closing actuating mechanism, electrically connected to the control circuit board and connected to and driving the operating mechanism; a first current detection device, configured to detect a current flowing through the first stationary contact, and electrically connected to the control circuit board; a second current detection device, configured to detect a current flowing through the second wiring terminal and the fourth wiring terminal, and electrically connected to the control circuit board; and an opening actuating mechanism, electrically connected to the second wiring terminal and the control circuit board, and configured to selectively drive the trip bar to be unlocked from the latch based on current information detected by the first current detection device and the second current detection device.