Abstract: A breathing apparatus has first bellows and second bellows, the first bellows being so designed as to expand by a part of air exhaled by the diver or wearer of the breathing apparatus being supplied thereto through a mouth piece and the second bellows being so designed as to contract as the pressure of a surrounding atmosphere around the breathing apparatus, i.e., the atmospheric pressure under water. When the sum of an expanded amount of the first bellows and a contracted amount of the second means reaches a value which is equal to or larger than a predetermined value, an exhalation discharge valve disposed on a mouth piece is so opened as to discharge the exhaled air into a surrounding atmosphere around the breathing apparatus. This arrangement for the breathing apparatus enables the number of times of re-utilizing the exhaled air as air for inhalation to increase as the pressure of the surrounding atmosphere increases.