An air conditioning system comprising a safety system including: a plurality of valve units used for a heat pump system, each of the valve units having at least one liquid refrigerant pipe portion, at least one gas refrigerant pipe portion, a casing formed with at least two openings (420, 430), and a refrigerant leakage detector configured to detect an occurrence of a refrigerant leakage in an internal space of the casing; and a discharge structure (720, 730) configured to discharge air from the internal space of the casing in which a refrigerant leakage has occurred, characterized in that: the air conditioning system further comprises a heatsource-side unit including a compressor and a heatsource-side heat exchanger, a plurality of utilization-side units each including a utilization-side heat exchanger, a liquid refrigerant piping extending between the heatsource-side unit and the utilization-side units, and including the liquid refrigerant pipe portions, a gas refrigerant piping extending between the heatsource-side unit and the utilization-side units, and including the gas refrigerant pipe portions, and an expansion mechanism disposed in the liquid refrigerant piping; each of the valve units further has at least one liquid control valve disposed in the liquid refrigerant pipe portion and at least one gas control valve disposed in the gas refrigerant pipe portion, wherein the casing of each of the valve units accommodates at least the liquid control valve and the gas control valve; the safety system further comprises a connection structure (710, 740a) connecting the internal spaces of the casings via the openings; and the discharge structure is connected to the connection structure or one of the casings. a safety system including: a plurality of valve units used for a heat pump system, each of the valve units having at least one liquid refrigerant pipe portion, at least one gas refrigerant pipe portion, a casing formed with at least two openings (420, 430), and a refrigerant leakage detector configured to detect an occurrence of a refrigerant leakage in an internal space of the casing; and a discharge structure (720, 730) configured to discharge air from the internal space of the casing in which a refrigerant leakage has occurred, a plurality of valve units used for a heat pump system, each of the valve units having at least one liquid refrigerant pipe portion, at least one gas refrigerant pipe portion, a casing formed with at least two openings (420, 430), and a refrigerant leakage detector configured to detect an occurrence of a refrigerant leakage in an internal space of the casing; and at least one liquid refrigerant pipe portion, at least one gas refrigerant pipe portion, a casing formed with at least two openings (420, 430), and a refrigerant leakage detector configured to detect an occurrence of a refrigerant leakage in an internal space of the casing; and a discharge structure (720, 730) configured to discharge air from the internal space of the casing in which a refrigerant leakage has occurred, characterized in that: the air conditioning system further comprises a heatsource-side unit including a compressor and a heatsource-side heat exchanger, a plurality of utilization-side units each including a utilization-side heat exchanger, a liquid refrigerant piping extending between the heatsource-side unit and the utilization-side units, and including the liquid refrigerant pipe portions, a gas refrigerant piping extending between the heatsource-side unit and the utilization-side units, and including the gas refrigerant pipe portions, and an expansion mechanism disposed in the liquid refrigerant piping; each of the valve units further has at least one liquid control valve disposed in the liquid refrigerant pipe portion and at least one gas control valve disposed in the gas refrigerant pipe portion, wherein the casing of each of the valve units accommodates at least the liquid control valve and the gas control valve; the safety system further comprises a connection structure (710, 740a) connecting the internal spaces of the casings via the openings; and the discharge structure is connected to the connection structure or one of the casings. the air conditioning system further comprises a heatsource-side unit including a compressor and a heatsource-side heat exchanger, a plurality of utilization-side units each including a utilization-side heat exchanger, a liquid refrigerant piping extending between the heatsource-side unit and the utilization-side units, and including the liquid refrigerant pipe portions, a gas refrigerant piping extending between the heatsource-side unit and the utilization-side units, and including the gas refrigerant pipe portions, and an expansion mechanism disposed in the liquid refrigerant piping; each of the valve units further has at least one liquid control valve disposed in the liquid refrigerant pipe portion and at least one gas control valve disposed in the gas refrigerant pipe portion, wherein the casing of each of the valve units accommodates at least the liquid control valve and the gas control valve; the safety system further comprises a connection structure (710, 740a) connecting the internal spaces of the casings via the openings; and the discharge structure is connected to the connection structure or one of the casings.