A breathing apparatus includes a compressed air source with a compressed air source valve, a breathing regulator with a pressure reducer and a demand valve, a breathing mask connected to the demand valve at a first inlet connector, a second air source, a switching mechanism having an actuating member for switching between the compressed air source and the second air source and an exhalation valve, on the breathing mask, movable between a higher internal pressure in a second operating state than in a first operating state. The actuating member is provided on the breathing regulator. The switching mechanism, upon being switching to compressed air breathing, activates the lung-governed demand valve and adjusts the exhalation valve to the second operating state. Upon switching to breathing via the second air source, the lung-governed demand valve is deactivated and the exhalation valve (30) is adjusted to the first operating state.