For the culture fluid and exopolysaccharide solution of the fungus Aureobasidium pullulans in a previous study, the angular frequency dependence of dynamic viscosity is well superimposed on the shear rate dependence of steady flow viscosity. For various polymeric fluids, the superimposition of the dependencies of steady flow viscosity and dynamic viscosity has also been realized. In this study, it is derived that, by assuming the sinusoidal oscillating flow of a viscoelastic fluid, complex viscosity is equivalent to viscosity in a steady flow measurement. A similar relation may also hold for the dynamic viscosity of an ideal viscous fluid. Generally, the measurement of the steady flow viscosity deprives a viscoelastic fluid of its elastic nature due to the disruption of the network structure causing the viscoelasticity. For the culture fluid and exopolysaccharide solution of A. pullulans, the correlation between the dynamic viscosity and the network structure was low. The dynamic viscosity in this case is consistent with the steady flow viscosity in the superimposing correlation.