Abstract: Provided is a common air conditioner operating system having a billing calculation function, including: at least one outdoor unit and a plurality of indoor units, at least one heat transfer unit, and a system operating apparatus configured to entirely control the above units, and calculate billing corresponding to use energy of each indoor unit, wherein the system operating apparatus sums a first amount obtained by multiplying a summed amount of a total heat production cost and a total heat transfer cost by a ratio of corresponding indoor unit supply heat si to a total supply heat S of all the indoor units, and heat supply costs of the corresponding indoor unit, and the total heat production cost is calculated by multiplying heat production energy, the total heat transfer cost is calculated by multiplying heat transfer energy, and the heat supply cost is calculated by multiplying heat supply energy.