A heat-pump using apparatus comprising: a refrigerant circuit configured to circulate refrigerant; a heat medium circuit configured to cause a heat medium to flow in the heat medium circuit; and a heat exchanger configured to cause heat exchange to be performed between the refrigerant and the heat medium, the heat medium circuit including a main circuit extending via the heat exchanger and a plurality of branch circuits (221, 222), the main circuit including a branching part located at a downstream end of the main circuit, and connected to those portions of the plurality of branch circuits (221, 222) which branch off from the main circuit, and a joining part located at an upstream end of the main circuit, and connected to those portions of the plurality of branch circuits (221, 222) which join the main circuit, the main circuit being provided as a circuit to which a pressure protection device, a connection part and a refrigerant leakage detecting device are connected, the refrigerant circuit including a first blocking device and a second blocking device between which the heat exchanger is located, the pressure protection device being connected to the connection part located between the heat exchanger and one of the branching part and the joining part in the main circuit, the refrigerant leakage detecting device being connected to the other of the branching part and the joining part, or between the connection part and the other of the branching part and the joining part, or to the connection part, in the main circuit, and the heat-pump using apparatus further comprising: an outdoor unit accommodating part of the refrigerant circuit; and an indoor unit accommodating a remaining part of the refrigerant circuit, the heat medium circuit and the heat exchanger, wherein the indoor unit further accommodates the first blocking device, the second blocking device and the refrigerant leakage detecting device. a refrigerant circuit configured to circulate refrigerant; a heat medium circuit configured to cause a heat medium to flow in the heat medium circuit; and a heat exchanger configured to cause heat exchange to be performed between the refrigerant and the heat medium, the heat medium circuit including a main circuit extending via the heat exchanger and a plurality of branch circuits (221, 222), the main circuit including a branching part located at a downstream end of the main circuit, and connected to those portions of the plurality of branch circuits (221, 222) which branch off from the main circuit, and a joining part located at an upstream end of the main circuit, and connected to those portions of the plurality of branch circuits (221, 222) which join the main circuit, a branching part located at a downstream end of the main circuit, and connected to those portions of the plurality of branch circuits (221, 222) which branch off from the main circuit, and a joining part located at an upstream end of the main circuit, and connected to those portions of the plurality of branch circuits (221, 222) which join the main circuit, the main circuit being provided as a circuit to which a pressure protection device, a connection part and a refrigerant leakage detecting device are connected, the refrigerant circuit including a first blocking device and a second blocking device between which the heat exchanger is located, the pressure protection device being connected to the connection part located between the heat exchanger and one of the branching part and the joining part in the main circuit, the refrigerant leakage detecting device being connected to the other of the branching part and the joining part, or between the connection part and the other of the branching part and the joining part, or to the connection part, in the main circuit, and the heat-pump using apparatus further comprising: an outdoor unit accommodating part of the refrigerant circuit; and an indoor unit accommodating a remaining part of the refrigerant circuit, the heat medium circuit and the heat exchanger, wherein the indoor unit further accommodates the first blocking device, the second blocking device and the refrigerant leakage detecting device.