A multi-air conditioner for heating/cooling operation, the multi-air conditioner comprising: at least one indoor unit for heating/cooling operation comprising an indoor heat exchanger respectively; and an outdoor unit for heating/cooling operation comprising a compressor, an outdoor heat exchanger (A1, A2), and a switching unit configured to be disposed in a discharge side of the compressor to switch a flow of refrigerant, wherein the outdoor unit for heating/cooling operation comprises: a receiver configured to selectively store refrigerant or oil according to a cooling or heating operation mode and to provide the stored refrigerant or oil to the compressor; a discharge pipe connected to a discharge portion of the compressor, an oil separator installed in the discharge pipe to recover oil from the refrigerant discharged from the compressor; a first oil recovery pipe connected to the oil separator, and guiding the oil separated from the oil separator to the compressor; an accumulator connected to the receiver and configured to transfer the refrigerant or oil to the compressor; a second oil recovery pipe connecting a lower side of the accumulator and an accumulator discharge pipe; an oil return valve disposed in the second oil recovery pipe to control the flow of oil; a receiver outlet pipe connecting the receiver and the accumulator; and a receiver inlet pipe for transferring the refrigerant to the receiver, wherein a receiver outlet valve is formed on the receiver outlet pipe and a receiver inlet valve is formed on the receiver inlet pipe, respectively, characterised by further comprising a receiver oil recovery pipe connecting the receiver and the first oil recovery pipe; an oil recovery valve formed in the receiver oil recovery pipe and configured to be opened and closed to recover the oil in the compressor to the receiver, wherein the receiver is configured to receive and store the oil from the compressor through the receiver oil recovery pipe in an oil recovery operation after a heating operation is terminated. at least one indoor unit for heating/cooling operation comprising an indoor heat exchanger respectively; and an outdoor unit for heating/cooling operation comprising a compressor, an outdoor heat exchanger (A1, A2), and a switching unit configured to be disposed in a discharge side of the compressor to switch a flow of refrigerant, wherein the outdoor unit for heating/cooling operation comprises: a receiver configured to selectively store refrigerant or oil according to a cooling or heating operation mode and to provide the stored refrigerant or oil to the compressor; a discharge pipe connected to a discharge portion of the compressor, an oil separator installed in the discharge pipe to recover oil from the refrigerant discharged from the compressor; a first oil recovery pipe connected to the oil separator, and guiding the oil separated from the oil separator to the compressor; an accumulator connected to the receiver and configured to transfer the refrigerant or oil to the compressor; a second oil recovery pipe connecting a lower side of the accumulator and an accumulator discharge pipe; an oil return valve disposed in the second oil recovery pipe to control the flow of oil; a receiver outlet pipe connecting the receiver and the accumulator; and a receiver inlet pipe for transferring the refrigerant to the receiver, wherein a receiver outlet valve is formed on the receiver outlet pipe and a receiver inlet valve is formed on the receiver inlet pipe, respectively, characterised by further comprising a receiver oil recovery pipe connecting the receiver and the first oil recovery pipe; an oil recovery valve formed in the receiver oil recovery pipe and configured to be opened and closed to recover the oil in the compressor to the receiver, wherein the receiver is configured to receive and store the oil from the compressor through the receiver oil recovery pipe in an oil recovery operation after a heating operation is terminated. a receiver configured to selectively store refrigerant or oil according to a cooling or heating operation mode and to provide the stored refrigerant or oil to the compressor; a discharge pipe connected to a discharge portion of the compressor, an oil separator installed in the discharge pipe to recover oil from the refrigerant discharged from the compressor; a first oil recovery pipe connected to the oil separator, and guiding the oil separated from the oil separator to the compressor; an accumulator connected to the receiver and configured to transfer the refrigerant or oil to the compressor; a second oil recovery pipe connecting a lower side of the accumulator and an accumulator discharge pipe; an oil return valve disposed in the second oil recovery pipe to control the flow of oil; a receiver outlet pipe connecting the receiver and the accumulator; and a receiver inlet pipe for transferring the refrigerant to the receiver, wherein a receiver outlet valve is formed on the receiver outlet pipe and a receiver inlet valve is formed on the receiver inlet pipe, respectively, characterised by further comprising a receiver oil recovery pipe connecting the receiver and the first oil recovery pipe; an oil recovery valve formed in the receiver oil recovery pipe and configured to be opened and closed to recover the oil in the compressor to the receiver, wherein the receiver is configured to receive and store the oil from the compressor through the receiver oil recovery pipe in an oil recovery operation after a heating operation is terminated.