This pressure compensating device for a volume of immersed gas is equipped with mobile or deformable walls and includes an immersed compensation bladder. The bladder is secured in a housing and communicates with the volume to be compensated. It is arranged by mounting means roughly at the level of the volume. According to the invention, the housing mounting means for the compensation bladder are arranged to allow the housing to move vertically relative to the gas volume so as to keep the mean front of the bladder folds at the level of the surfaces to be compensated, as the volume may be immersed to different depths.The housing mounting means include an arm hinged about a horizontal axis, and a spring exerting its force on a cable connected to the hinged arm.Depending on the preferred application, the mobile walls enclosing volume to be compensated consist of the acoustic drives of underwater electroacoustic transducers.