A compression mechanism has a cylinder, a suction passage and a discharge passage. The suction passage of a cylinder is connected to a suction pipe. The discharge passage is open to an inner space of a sealed housing. A discharge gas is discharged through a discharge pipe. The cylinder is formed with a communicating passage extending from a suction passage to a suction pressure chamber to lead a suction gas in the suction passage into the suction pressure chamber and thereby allow a pressure of the suction gas in the suction passage to act on an outside surface of the cylinder.