A unitary air conditioner comprises a 1-stage thermostat for generating an operation signal for the unitary air conditioner or a stop signal for the unitary air conditioner, a 1-stage indoor unit having an indoor fan, which is rotated according the operation signal from the 1-stage thermostat, a variable-capacity outdoor unit configured to be operated according to the 1-stage thermostat, the variable-capacity outdoor unit having a compressor and an outdoor fan, the operation stage of which is changed according to the operation state of the variable-capacity outdoor unit, and an indoor fan control device for controlling the indoor fan according to the operation stage of the variable-capacity outdoor unit to change the operation state of the indoor fan. The 1-stage indoor unit is operated along with another unit having different stages, and variable control is accomplished, although the 1-stage indoor unit is used, so long as the indoor fan control device is added to the unitary air conditioner. Consequently, a more efficient air conditioning system is accomplished.