Heating medium compression apparatus, air conditioner, and heating medium compression method

A heating medium compression apparatus comprising:

• a first compressor and a second compressor that compress a heating medium;
• a suction side piping and a discharge side piping that connect the first compressor and the second compressor to a heat exchanger;
• a connection piping that connects a discharge side of the first compressor and a suction side of the second compressor in series;
• and
• a control unit that controls a flow rate of the heating medium flowing in the suction side piping, the discharge side piping, and the connection piping,
• wherein the control unit alternatively connects the first compressor or the second compressor to the suction side piping and the discharge side piping or connects the first compressor and the second compressor in series between the suction side piping and the discharge side piping and performs control such that the flow rate of the heating medium suctioned into the second compressor connected in series becomes higher than the flow rate of the heating medium discharged from the first compressor.