An air conditioner comprising: a plurality of indoor units; and at least one outdoor unit; wherein the outdoor unit comprises: a compressor (1, 131): an accumulator configured to recover a liquid refrigerant contained in a refrigerant flowing into the compressor (1, 131); an outdoor heat exchanger configured to perform heat exchange of air using the refrigerant; an outdoor unit fan configured to supply outside air to the outdoor heat exchanger and discharging heat-exchanged air; a refrigerant charging pipe connected to a refrigerant pipe and allowing the refrigerant to be additionally introduced from the outside; a refrigerant charging valve installed in the refrigerant charging pipe to open and close the refrigerant charging pipe; and a controller configured to set an operation mode so as to operate in a cooling operation or heating operation upon setting of a refrigerant charging mode, to set an operation frequency of the compressor (1, 131) in accordance with a load of the plurality of indoor units upon the setting of the refrigerant charging mode to allow the compressor (1, 131) to operate at the set operation frequency during the refrigerant charging, and to calculate the amount of refrigerant to stop the refrigerant charging when a predetermined reference value is reached, characterized in that, the refrigerant charging pipe is connected to the refrigerant pipe at which refrigerant flows into the accumulator, the controller in operation is configured to set the refrigerant charging mode for the heating operation or the refrigerant charging mode for the cooling operation according to the respective operation mode; and the controller in the operation stop state is configured to set the operation mode, based on the indoor temperature and the outdoor temperature. a plurality of indoor units; and at least one outdoor unit; wherein the outdoor unit comprises: a compressor (1, 131): an accumulator configured to recover a liquid refrigerant contained in a refrigerant flowing into the compressor (1, 131); an outdoor heat exchanger configured to perform heat exchange of air using the refrigerant; an outdoor unit fan configured to supply outside air to the outdoor heat exchanger and discharging heat-exchanged air; a refrigerant charging pipe connected to a refrigerant pipe and allowing the refrigerant to be additionally introduced from the outside; a refrigerant charging valve installed in the refrigerant charging pipe to open and close the refrigerant charging pipe; and a controller configured to set an operation mode so as to operate in a cooling operation or heating operation upon setting of a refrigerant charging mode, to set an operation frequency of the compressor (1, 131) in accordance with a load of the plurality of indoor units upon the setting of the refrigerant charging mode to allow the compressor (1, 131) to operate at the set operation frequency during the refrigerant charging, and to calculate the amount of refrigerant to stop the refrigerant charging when a predetermined reference value is reached, characterized in that, the refrigerant charging pipe is connected to the refrigerant pipe at which refrigerant flows into the accumulator, the controller in operation is configured to set the refrigerant charging mode for the heating operation or the refrigerant charging mode for the cooling operation according to the respective operation mode; and the controller in the operation stop state is configured to set the operation mode, based on the indoor temperature and the outdoor temperature. a compressor (1, 131): an accumulator configured to recover a liquid refrigerant contained in a refrigerant flowing into the compressor (1, 131); an outdoor heat exchanger configured to perform heat exchange of air using the refrigerant; an outdoor unit fan configured to supply outside air to the outdoor heat exchanger and discharging heat-exchanged air; a refrigerant charging pipe connected to a refrigerant pipe and allowing the refrigerant to be additionally introduced from the outside; a refrigerant charging valve installed in the refrigerant charging pipe to open and close the refrigerant charging pipe; and a controller configured to set an operation mode so as to operate in a cooling operation or heating operation upon setting of a refrigerant charging mode, to set an operation frequency of the compressor (1, 131) in accordance with a load of the plurality of indoor units upon the setting of the refrigerant charging mode to allow the compressor (1, 131) to operate at the set operation frequency during the refrigerant charging, and to calculate the amount of refrigerant to stop the refrigerant charging when a predetermined reference value is reached, characterized in that, the refrigerant charging pipe is connected to the refrigerant pipe at which refrigerant flows into the accumulator, the controller in operation is configured to set the refrigerant charging mode for the heating operation or the refrigerant charging mode for the cooling operation according to the respective operation mode; and the controller in the operation stop state is configured to set the operation mode, based on the indoor temperature and the outdoor temperature.