Breathing apparatus comprising a face piece for covering the whole face of a user and a fan unit for operating synchronously with the breath timing of the user. The breathing apparatus comprises a breath monitoring apparatus provided with a diaphragm and a sensor for detecting movement of the diaphragm. The location of the diaphragm and the sensor and a transmission path of inhale pressure and exhale pressure to the diaphragm are optimized. The breath monitoring apparatus is disposed in a fan unit, a space for accommodating the diaphragm and the sensor is disposed independently of an air passage in the fan unit, and the internal space of a nose cup is communicated with the space in the fan unit through holes formed in the nose cup and the face piece when the fan unit and the nose cup are connected to the face piece.