A refrigerant circuit for an air conditioner of heat pump type comprising an outdoor unit and an indoor unit, the outdoor unit and the indoor unit being connected by a liquid side refrigerant pipe and a gas-side refrigerant pipe; the indoor unit comprising an indoor heat exchanger, and an indoor blowing fan; and the outdoor unit comprising a four-way valve, an outdoor heat exchanger, an outdoor blowing fan, an outdoor expansion valve, and a rotary compressor comprising: a compressor body including an airtight container that has a refrigerant intake opening and a refrigerant discharge opening, a refrigerant compression unit that has a cylinder and a rotary piston housed in the cylinder and that is provided in the airtight container, and an electric motor that drives the rotary piston and is provided in the airtight container; and an accumulator configured to separate a refrigerant suctioned into the refrigerant intake opening into gas and liquid, wherein the accumulator and the refrigerant intake opening are connected via a refrigerant intake pipe, a suction opening of the refrigerant intake pipe is arranged to be opened to an inside of the accumulator, an injection pipe together with a refrigerant return pipe are inserted into the accumulator from above, wherein the refrigerant return pipe is configured to return a low-pressure refrigerant to the accumulator; and characterized in that the refrigerant return pipe is configured to return the low-pressure refrigerant to the accumulator via the gas-side refrigerant pipe, and the injection pipe is branched from the liquid-side refrigerant pipe at a position of said liquid-side refrigerant pipe on an upstream side of the outdoor expansion valve during heating operation; and a discharge opening of the injection pipe is drawn to face the suction opening of the refrigerant intake pipe in a refrigerant gas space of the accumulator. a compressor body including an airtight container that has a refrigerant intake opening and a refrigerant discharge opening, a refrigerant compression unit that has a cylinder and a rotary piston housed in the cylinder and that is provided in the airtight container, and an electric motor that drives the rotary piston and is provided in the airtight container; and an accumulator configured to separate a refrigerant suctioned into the refrigerant intake opening into gas and liquid, wherein the accumulator and the refrigerant intake opening are connected via a refrigerant intake pipe, a suction opening of the refrigerant intake pipe is arranged to be opened to an inside of the accumulator, an injection pipe together with a refrigerant return pipe are inserted into the accumulator from above, wherein the refrigerant return pipe is configured to return a low-pressure refrigerant to the accumulator; and characterized in that the refrigerant return pipe is configured to return the low-pressure refrigerant to the accumulator via the gas-side refrigerant pipe, and the injection pipe is branched from the liquid-side refrigerant pipe at a position of said liquid-side refrigerant pipe on an upstream side of the outdoor expansion valve during heating operation; and a discharge opening of the injection pipe is drawn to face the suction opening of the refrigerant intake pipe in a refrigerant gas space of the accumulator.