A pressure compensation unit and a variable capacity type axis-compressing device including the same are provided to keep the charged capacity of working fluid, charged inside an accumulator, regular. A pressure compensation unit comprises: a housing(100) having regular length and a specific internal space; a bellows(120) of regular length connected with the internal space, installed at an one end part of the housing; and a controlling unit compensating for the inside pressure by varying the volume of the internal space of the housing relative to the temperature of the outside. |