Internal friction behavior of the standard anelastic solid has been described by τσ (the relaxation time at constant stress) and τε (the relaxation time at constant strain) of a three-parameter mechanical model. The effect of the inertia member in a vibration system on the internal friction values measured is not avoidable in a forced vibration experiment. When the measured internal friction values of a material are larger and the measuring frequency and resonant frequency of the vibration system are comparable to each other, the effect of the inertia member of the vibration system cannot be neglected.