A refrigerant filling apparatus for filling a refrigerant circuit of a refrigerating and air conditioning apparatus with a refrigerant, the refrigerant circuit having a compressor, a four-way valve, an indoor side heat exchanger, a pressure reducing apparatus, an outdoor side heat exchanger, and a liquid collecting device; wherein the refrigerant filling apparatus comprises: a refrigerant cylinder connectable to a low pressure side of the refrigerant circuit with a valve between the refrigerating and air conditioning apparatus and the refrigerant cylinder; a control unit adapted to: control refrigerant filling from the refrigerant cylinder to the refrigerant circuit wherein the refrigerant filling controlled by the control unit is configured such that the refrigerant is filled from the refrigerant cylinder to the refrigerant circuit while the refrigerating and air conditioning apparatus is in operation characterised in that the control unit is adapted to: set an operation mode of the refrigerant circuit to one of a heating operation or a cooling operation in which the refrigerant exists in a liquid state in a liquid side connection pipe that connects an indoor unit including the indoor side heat exchanger and an outdoor unit including the outdoor side heat exchanger for use as a filling mode when deciding whether or not a refrigerant amount in the refrigeration circuit is normal; wherein the refrigerant filling apparatus further comprises: a display unit adapted to display the filling mode of the refrigerant, which is mounted to the control unit; wherein the refrigerant filling controlled by the control unit is configured such that the compressor is automatically stopped and the four-way valve is switched and the pressure reducing apparatus is opened so that pressure inside the refrigerant circuit becomes uniform when the refrigerant amount is decided to be normal. a refrigerant cylinder connectable to a low pressure side of the refrigerant circuit with a valve between the refrigerating and air conditioning apparatus and the refrigerant cylinder; a control unit adapted to: control refrigerant filling from the refrigerant cylinder to the refrigerant circuit wherein the refrigerant filling controlled by the control unit is configured such that the refrigerant is filled from the refrigerant cylinder to the refrigerant circuit while the refrigerating and air conditioning apparatus is in operation control refrigerant filling from the refrigerant cylinder to the refrigerant circuit wherein the refrigerant filling controlled by the control unit is configured such that the refrigerant is filled from the refrigerant cylinder to the refrigerant circuit while the refrigerating and air conditioning apparatus is in operation characterised in that the control unit is adapted to: set an operation mode of the refrigerant circuit to one of a heating operation or a cooling operation in which the refrigerant exists in a liquid state in a liquid side connection pipe that connects an indoor unit including the indoor side heat exchanger and an outdoor unit including the outdoor side heat exchanger for use as a filling mode when deciding whether or not a refrigerant amount in the refrigeration circuit is normal; wherein the refrigerant filling apparatus further comprises: a display unit adapted to display the filling mode of the refrigerant, which is mounted to the control unit; wherein the refrigerant filling controlled by the control unit is configured such that the compressor is automatically stopped and the four-way valve is switched and the pressure reducing apparatus is opened so that pressure inside the refrigerant circuit becomes uniform when the refrigerant amount is decided to be normal. set an operation mode of the refrigerant circuit to one of a heating operation or a cooling operation in which the refrigerant exists in a liquid state in a liquid side connection pipe that connects an indoor unit including the indoor side heat exchanger and an outdoor unit including the outdoor side heat exchanger for use as a filling mode when deciding whether or not a refrigerant amount in the refrigeration circuit is normal; wherein the refrigerant filling apparatus further comprises: a display unit adapted to display the filling mode of the refrigerant, which is mounted to the control unit; wherein the refrigerant filling controlled by the control unit is configured such that the compressor is automatically stopped and the four-way valve is switched and the pressure reducing apparatus is opened so that pressure inside the refrigerant circuit becomes uniform when the refrigerant amount is decided to be normal. a display unit adapted to display the filling mode of the refrigerant, which is mounted to the control unit; wherein the refrigerant filling controlled by the control unit is configured such that the compressor is automatically stopped and the four-way valve is switched and the pressure reducing apparatus is opened so that pressure inside the refrigerant circuit becomes uniform when the refrigerant amount is decided to be normal.