An air conditioning system of the present invention has a refrigerant circuit including a compressor, an oil separator, a condenser, a expansion device, an evaporator, a first accumulator, and a second accumulator which are connected in order by piping, said evaporator, said first accumulator, said second accumulator, and said compressor being connected in series; a first oil return bypass for connecting said oil separator and a connection pipe between said first and second accumulators; and a second oil return bypass for connecting said first accumulator and a connection pipe between said second accumulator and said compressor.