The embodiment of the present invention provides a system which calculates the flow rates of flow meters by adopting a plurality of modes, comprising a device which calibrates the flow meter for a plurality of ideal modes, a device which confirms the density of substances which are relevant to the ideal modes and flow through the flow meter, further a device which confirms the effects that flow rates have on density for a plurality of ideal modes and a device which calculates the flow rates on the basis of the effects which the density and flow rates of the ideal modes have on the density values.