Provided is an air-conditioner refrigerant injecting method that enables precise and quick injection of an optimum amount of refrigerant . In an air-conditioner (1) refrigerant injecting method of injecting a specified amount of refrigerant into a closed-cycle refrigerant circuit (3) in which an outdoor unit (10) and a plurality of indoor units (11) to (16) are connected via refrigerant pipes (2), the pipe lengths and pipe diameters of the refrigerant pipes (2A) to (2M) connecting the outdoor unit (10) and the plurality of indoor units (11) to (16) installed on the respective floors of a structure (40) are identified insofar as they can be reliably measured or estimated, the minimum required refrigerant amount required by the air conditioner (1) is calculated on the basis of the pipe lengths and pipe diameters, the resulting amount of refrigerant is additionally injected in advance, and then the refrigerant is automatically injected by an automatic refrigerant injection function until a specified injection amount is reached.