An apparatus using a heat pump, the apparatus comprising: a refrigerant circuit including a compressor, a refrigerant flow switching device, a heat-source-side heat exchanger, an expansion device, a load-side heat exchanger, and a container, the refrigerant circuit being configured to circulate refrigerant; and a heat medium circuit configured to cause a heat medium to flow via the load-side heat exchanger, the refrigerant flow switching device being configured in such a manner that a state of the refrigerant flow switching device is switchable between a first state and a second state, the refrigerant circuit being allowed to perform a first operation in which the load-side heat exchanger is used as a condenser, when the state of the refrigerant flow switching device is switched to the first state, the refrigerant circuit being allowed to perform a second operation in which the load-side heat exchanger is used as an evaporator, when the state of the refrigerant flow switching device is switched to the second state, the container being provided to a suction pipe provided between the refrigerant flow switching device and the compressor, the heat medium circuit including a main circuit extending via the load-side heat exchanger, the main circuit including a branching part provided at a downstream end of the main circuit, the branching part being a part at which a plurality of branch circuits that branch off from the main circuit are connected, and a joining part provided at an upstream end of the main circuit, the joining part being a part at which the plurality of branch circuits are connected to join the main circuit, to the heat medium circuit, an overpressure protection device being connected, in the main circuit, the overpressure protection device being connected to a connection part that is located between the load-side heat exchanger and one of the branching part and the joining part or at the load-side heat exchanger, characterised by a refrigerant leakage detecting device being connected, in the main circuit, the refrigerant leakage detecting device being connected between the connection part and the other of the branching part and the joining part, or to the connection part; or to the other of the branching part and the joining part, when leakage of the refrigerant into the heat medium circuit is detected, the refrigerant flow switching device being switched to the second state, the expansion device being set to a closed state, and the compressor being made in operation, when a requirement for ending the operation of the compressor is satisfied after the leakage of the refrigerant into the heat medium circuit is detected, the compressor being set to a stopped state, and the refrigerant flow switching device being switched to the first state. a refrigerant circuit including a compressor, a refrigerant flow switching device, a heat-source-side heat exchanger, an expansion device, a load-side heat exchanger, and a container, the refrigerant circuit being configured to circulate refrigerant; and a heat medium circuit configured to cause a heat medium to flow via the load-side heat exchanger, the refrigerant flow switching device being configured in such a manner that a state of the refrigerant flow switching device is switchable between a first state and a second state, the refrigerant circuit being allowed to perform a first operation in which the load-side heat exchanger is used as a condenser, when the state of the refrigerant flow switching device is switched to the first state, the refrigerant circuit being allowed to perform a second operation in which the load-side heat exchanger is used as an evaporator, when the state of the refrigerant flow switching device is switched to the second state, the container being provided to a suction pipe provided between the refrigerant flow switching device and the compressor, the heat medium circuit including a main circuit extending via the load-side heat exchanger, the main circuit including a branching part provided at a downstream end of the main circuit, the branching part being a part at which a plurality of branch circuits that branch off from the main circuit are connected, and a joining part provided at an upstream end of the main circuit, the joining part being a part at which the plurality of branch circuits are connected to join the main circuit, to the heat medium circuit, an overpressure protection device being connected, in the main circuit, the overpressure protection device being connected to a connection part that is located between the load-side heat exchanger and one of the branching part and the joining part or at the load-side heat exchanger, characterised by a refrigerant leakage detecting device being connected, in the main circuit, the refrigerant leakage detecting device being connected between the connection part and the other of the branching part and the joining part, or to the connection part; or to the other of the branching part and the joining part, when leakage of the refrigerant into the heat medium circuit is detected, the refrigerant flow switching device being switched to the second state, the expansion device being set to a closed state, and the compressor being made in operation, when a requirement for ending the operation of the compressor is satisfied after the leakage of the refrigerant into the heat medium circuit is detected, the compressor being set to a stopped state, and the refrigerant flow switching device being switched to the first state.