An internal intermediate pressure 2-stage compression type rotary compressor (10), which comprises an electrically-driven element (14) in a closed vessel (12), and first and second rotary compression elements (32, 34) driven by the electrically-driven element (14), wherein CO2 coolant gas subjected to first-stage compression by the first rotary compression element (32) is discharged into the closed vessel (12) and the discharged coolant gas of intermediate pressure is passed through an accumulator (106) and subjected to second-stage compression by the second rotary compression element (34), the rotary compression elements (32, 34) comprising upper and lower cylinders (38, 40), upper and lower rollers (46, 48) eccentrically rotating within the cylinders, upper and lower vanes (50, 52) contacting the rollers and partitioning the upper and lower cylinders into higher and lower pressure chambers, the volume ratio of the upper and lower cylinders (38, 40) for first and second stage compression being set at 1 : 0.65 so that the equilibrium pressure and the intermediate pressure are equal. Since the pressure variation at the start of operation is low, oil forming is suppressed and the pressure vessel is easy to design and can be reduced in weight.