A polyphase (e.g., three-phase) metal-enclosed, gas-insulated high-voltage circuit breaker and a switchgear including the circuit breaker is provided. For each phase, the circuit breaker includes one power arcing chamber pole per phase which are accommodated together in a common circuit breaker housing, and which have at least two connecting outputs per phase. The circuit breaker housing has a number, corresponding to the number of arcing chamber poles of chambers open at their front ends, in which the arcing chamber poles are arranged. The open front ends of the chambers are each respectively closed by means a corresponding dome-like lid covering the corresponding front ends so that a gas link between the individual chambers is provided for via the connection spaces created by the lids.