An air conditioner comprising: an outdoor unit including a compressor; a plurality of indoor units (3a, 3b, 3c, 3d), each including an indoor expansion valve (51a, 51b, 51c, 51d) and an indoor heat exchanger (52a, 52b, 52c, 52d); a liquid-refrigerant connection pipe and a gas-refrigerant connection pipe that connect the outdoor unit and the indoor units to each other; a plurality of relay units (4a, 4b, 4c, 4d), which are respectively connected to the indoor units (3a, 3b, 3c, 3d) and disposed in the liquid-refrigerant connection pipe and the gas-refrigerant connection pipe, each relay unit including a liquid relay shut-off valve (71a, 71b, 71c, 71d) in a liquid connection pipe (61a, 61b, 61c, 61d) connected to the liquid-refrigerant connection pipe and a gas relay shut-off valve (66a, 66b, 66c, 66d, 67a, 67b, 67c, 67d) in a gas connection pipe (62a, 62b, 62c, 62d) connected to the gas-refrigerant connection pipe, each relay unit being configured to individually switch an indoor heat exchanger so that the indoor heat exchanger is capable of functioning as an evaporator for refrigerant or a radiator for the refrigerant; refrigerant leakage detection means (79a, 79b, 79c, 79d) for detecting leakage of the refrigerant; and a control unit configured to control components of the outdoor unit, the indoor units, and the relay unit, characterized in that the control unit is configured to, when leakage of the refrigerant occurs, perform first shut-off control to open a liquid relay shut-off valve and close an indoor expansion valve and a gas relay shutoff valve on the basis of information from the refrigerant leakage detection means to separate a portion between the indoor expansion valve and the gas relay shut-off valve including the indoor heat exchanger from which refrigerant is likely to leak. an outdoor unit including a compressor; a plurality of indoor units (3a, 3b, 3c, 3d), each including an indoor expansion valve (51a, 51b, 51c, 51d) and an indoor heat exchanger (52a, 52b, 52c, 52d); a liquid-refrigerant connection pipe and a gas-refrigerant connection pipe that connect the outdoor unit and the indoor units to each other; a plurality of relay units (4a, 4b, 4c, 4d), which are respectively connected to the indoor units (3a, 3b, 3c, 3d) and disposed in the liquid-refrigerant connection pipe and the gas-refrigerant connection pipe, each relay unit including a liquid relay shut-off valve (71a, 71b, 71c, 71d) in a liquid connection pipe (61a, 61b, 61c, 61d) connected to the liquid-refrigerant connection pipe and a gas relay shut-off valve (66a, 66b, 66c, 66d, 67a, 67b, 67c, 67d) in a gas connection pipe (62a, 62b, 62c, 62d) connected to the gas-refrigerant connection pipe, each relay unit being configured to individually switch an indoor heat exchanger so that the indoor heat exchanger is capable of functioning as an evaporator for refrigerant or a radiator for the refrigerant; refrigerant leakage detection means (79a, 79b, 79c, 79d) for detecting leakage of the refrigerant; and a control unit configured to control components of the outdoor unit, the indoor units, and the relay unit, characterized in that the control unit is configured to, when leakage of the refrigerant occurs, perform first shut-off control to open a liquid relay shut-off valve and close an indoor expansion valve and a gas relay shutoff valve on the basis of information from the refrigerant leakage detection means to separate a portion between the indoor expansion valve and the gas relay shut-off valve including the indoor heat exchanger from which refrigerant is likely to leak.