A refrigeration system, comprising a compressor, a flow path switching mechanism for switching a circulation direction of a refrigerant discharged from the compressor, an outdoor heat exchanger, an expansion valve capable of being fully closed, and an indoor heat exchanger, which are connected to one another by a refrigerant pipe, the refrigeration system further comprising: a receiver provided upstream of the expansion valve; a gas vent passageway for connecting the receiver and a downstream side pipe of the expansion valve to each other; gas vent opening/closing means provided along the gas vent passageway; control means; and a bridge circuit, wherein during a cooling operation, the bridge circuit only allows a refrigerant flow in such a direction as to lead the refrigerant, which has been condensed through the outdoor heat exchanger, to the receiver and a refrigerant flow in such a direction as to lead the refrigerant, which has been depressurized through the expansion valve, to the indoor heat exchanger, and during a heating operation, the bridge circuit only allows a refrigerant flow in such a direction as to lead the refrigerant, which has been condensed through the indoor heat exchanger, to the receiver and a refrigerant flow in such a direction as to lead the refrigerant, which has been depressurized through the expansion valve, to the outdoor heat exchanger, wherein: at least the following elements are provided on an outdoor side: the receiver; a path extending from the receiver to the expansion valve; a path extending from a circuit section in the bridge circuit to the receiver, the circuit section only allowing a refrigerant flow in such a direction as to lead the refrigerant, which has been condensed through the outdoor heat exchanger, to the receiver during a cooling operation; a path extending from a circuit section in the bridge circuit to the receiver, the circuit section only allowing a refrigerant flow in such a direction as to lead the refrigerant, which has been condensed through the indoor heat exchanger, to the receiver during a heating operation; and a path along the gas vent passageway extending from the receiver to the gas vent opening/closing means; characterized in that the control means, before shutting down the compressor, opens the gas vent opening/closing means and closes the expansion valve while the compressor is left operating, and closes the gas vent opening/closing means upon subsequent shut down of the compressor. a receiver provided upstream of the expansion valve; a gas vent passageway for connecting the receiver and a downstream side pipe of the expansion valve to each other; gas vent opening/closing means provided along the gas vent passageway; control means; and a bridge circuit, wherein during a cooling operation, the bridge circuit only allows a refrigerant flow in such a direction as to lead the refrigerant, which has been condensed through the outdoor heat exchanger, to the receiver and a refrigerant flow in such a direction as to lead the refrigerant, which has been depressurized through the expansion valve, to the indoor heat exchanger, and during a heating operation, the bridge circuit only allows a refrigerant flow in such a direction as to lead the refrigerant, which has been condensed through the indoor heat exchanger, to the receiver and a refrigerant flow in such a direction as to lead the refrigerant, which has been depressurized through the expansion valve, to the outdoor heat exchanger, wherein: at least the following elements are provided on an outdoor side: the receiver; a path extending from the receiver to the expansion valve; a path extending from a circuit section in the bridge circuit to the receiver, the circuit section only allowing a refrigerant flow in such a direction as to lead the refrigerant, which has been condensed through the outdoor heat exchanger, to the receiver during a cooling operation; a path extending from a circuit section in the bridge circuit to the receiver, the circuit section only allowing a refrigerant flow in such a direction as to lead the refrigerant, which has been condensed through the indoor heat exchanger, to the receiver during a heating operation; and a path along the gas vent passageway extending from the receiver to the gas vent opening/closing means; characterized in that the control means, before shutting down the compressor, opens the gas vent opening/closing means and closes the expansion valve while the compressor is left operating, and closes the gas vent opening/closing means upon subsequent shut down of the compressor. at least the following elements are provided on an outdoor side: the receiver; a path extending from the receiver to the expansion valve; a path extending from a circuit section in the bridge circuit to the receiver, the circuit section only allowing a refrigerant flow in such a direction as to lead the refrigerant, which has been condensed through the outdoor heat exchanger, to the receiver during a cooling operation; a path extending from a circuit section in the bridge circuit to the receiver, the circuit section only allowing a refrigerant flow in such a direction as to lead the refrigerant, which has been condensed through the indoor heat exchanger, to the receiver during a heating operation; and a path along the gas vent passageway extending from the receiver to the gas vent opening/closing means; characterized in that the control means, before shutting down the compressor, opens the gas vent opening/closing means and closes the expansion valve while the compressor is left operating, and closes the gas vent opening/closing means upon subsequent shut down of the compressor.